A Block Chain — historically called Galle Chain after its inventor André Galle — is a stacked-plate tension chain built from alternating side plates joined by hardened pins, with no rollers or bushings. Forklift and lift-truck builders rely on it for mast hoist duty because it carries pure tensile load over a sheave, not around a sprocket. The side-plate stack spreads load across many shear planes, giving very high ultimate tensile strength in a thin profile. A typical BL1244 leaf chain handles roughly 65 kN working load on a 38.1 mm pitch.
Block Chain (Galle Chain) Drive Interactive Calculator
Vary chain strength, safety factor, applied tensile load, shear planes, and pitch to see allowable working load and load sharing over a smooth sheave.
Equation Used
The calculator applies the leaf-chain working-load rule Fw = FUTS / SF. FUTS is the catalogue ultimate tensile strength and SF is the selected safety factor. Utilization compares the applied tensile load to the allowable working load, while load per plane estimates how the pin load is shared across the active shear planes.
- Chain carries pure tensile load over a smooth sheave.
- Allowable working load is ultimate tensile strength divided by safety factor.
- Pin shear load is estimated as applied load divided by active shear planes.
- Dynamic shock, wear, lubrication, and bending fatigue are not included.
How the Block Chain (galle Chain) Drive Works
A Block Chain transmits force the way a flat steel cable transmits force — in pure tension, along its length. It does not wrap a toothed sprocket and it does not need to articulate around small radii at high speed. The chain is built up from flat side plates stacked in lacing patterns like 2×3, 3×4, 4×6, 6×6, depending on how much load you need to carry. Hardened steel pins pass through aligned holes in those plates and rivet over on the outside. When you load the chain, every pin sits in double, triple or quadruple shear and every plate carries part of the tensile load through its cross-section between the holes. That is why a leaf chain in a forklift mast can hold a 5,000 lb pallet on a thin two-strand assembly hanging off a hydraulic ram — the load path is plates and pins, nothing else.
The geometry has to be exact or the chain self-destructs. Pitch — the centre-to-centre distance between pins — must hold to roughly ±0.05 mm across the working length, otherwise some plates carry more than their share and you get plate cracking at the hole. Pin fit in the outer plates is an interference press, not a slip fit; a loose pin walks out under cyclic load and you lose the strand. The articulation between an inner plate and a pin is a plain metal-on-metal sliding joint, so the chain elongates over time as the pin and the plate hole both wear. Elongation past 3% of nominal pitch is the standard retirement criterion in lift-truck service — measure ten pitches with calipers, compare to the nameplate, and if you are over 3% the chain comes off, no exception.
Why no rollers? Because Block Chain is not running around a sprocket at speed. It runs over a smooth sheave, the same way a wire rope runs over a sheave. Roller chain needs rollers because the rollers seat into sprocket teeth and reduce sliding friction at engagement. A Block Chain over a forklift mast sheave only flexes once per cycle, at the sheave, so the sliding friction at the pin is acceptable and the rollers would just add cost, weight and failure modes.
Key Components
- Side Plates (Link Plates): Flat hardened steel plates with two precision-bored holes at the chain pitch. Plates carry the tensile load through their net section between the holes — typically 40 to 50 HRC after heat treatment. Hole spacing tolerance is held to ±0.05 mm so load shares evenly across the lacing pattern.
- Pins: Hardened, ground steel pins that pass through the stacked plates and rivet on the outside. Pins sit in double, triple or quadruple shear depending on the lacing. Pin-to-outer-plate fit is an interference press; pin-to-inner-plate fit is a running clearance that allows articulation at the sheave.
- Lacing Pattern: Designation like 2×2, 3×4, 4×4, 6×6 that describes how many plates sit on each side of each pin. Heavier lacing means more shear planes and higher allowable working load. A BL844 chain is a 4×4 lacing on a 25.4 mm pitch and carries roughly 36 kN working load.
- Sheave: Smooth grooved pulley the chain runs over — not a toothed sprocket. Sheave diameter typically sits at 8 to 12 times the chain pitch to keep articulation angles low and reduce pin wear. Undersizing the sheave is one of the fastest ways to kill a leaf chain.
- Anchor / Clevis End Fittings: Forged steel clevis or stud-link terminations that pin the chain to the load and to the dead end. Rated to the same ultimate tensile strength as the chain itself. A failed anchor is just as catastrophic as a failed chain — both ends get inspected at the same interval.
Industries That Rely on the Block Chain (galle Chain) Drive
Block Chain shows up wherever you need a thin, flexible, very-high-tensile-strength member that runs over a sheave instead of a sprocket. The dominant modern application is forklift and aerial-lift mast hoists, but the same chain family — under the BL and LH designations in ANSI B29.8 — appears across material handling, presses, and balanced-load lifting equipment.
- Material Handling: Toyota 8FGCU25 and Hyster H50FT forklift mast hoists run BL-series leaf chain in pairs over crown sheaves at the top of each mast stage, lifting pallet loads up to 5,000 lb.
- Aerial Work Platforms: JLG and Genie telescoping boom lifts use leaf chain inside the boom sections to extend and retract the inner sections under load.
- Metal Forming: Counterweight chains on Bliss and Schuler mechanical stamping presses, balancing the slide weight against the press frame so the brake doesn't have to hold the slide statically.
- Industrial Doors: High-speed roll-up door counterbalance systems on cold-storage and aircraft hangar doors, where the chain offsets the curtain weight against a torsion drum.
- Historical Machinery: Late-1800s factory line shafting and crane hoists — the original Galle Chain, patented in France in 1829 by André Galle, ran on the cranes and lifts of early industrial mills before wire rope took over for long-travel applications.
- Theatrical & Stage Rigging: Counterweight assist systems in fly towers where load capacity per cross-section is more important than wrap radius.
The Formula Behind the Block Chain (galle Chain) Drive
The number that drives every leaf-chain selection is working load — the tensile force you can put on the chain continuously without exceeding the design safety factor against ultimate tensile strength. At the low end of typical mast service, you might be running a single chain pair at 25% of its working load, which gives effectively unlimited fatigue life and almost no measurable elongation per year. At the nominal design point — usually 80% of working load on a fully loaded forklift — you trade fatigue life for capacity but stay inside the standard 5:1 safety factor. Push past 100% of working load and you erode that safety factor fast, which is why ANSI B29.8 caps allowable working load at UTS divided by 5 for lift duty.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Fw | Allowable working load on the chain | N (or kN) | lbf |
| FUTS | Ultimate tensile strength of the chain (catalogue value) | N (or kN) | lbf |
| SF | Safety factor — 5 for lift duty per ANSI B29.8, higher for personnel-rated systems | dimensionless | dimensionless |
| Le | Elongation, expressed as percentage of nominal pitch — 3% is the retirement limit | % | % |
Worked Example: Block Chain (galle Chain) Drive in a 4,500 lb-capacity electric forklift mast
You are sizing the lift chain pair on a new 4,500 lb-capacity Class I electric forklift you are building for a beverage distribution warehouse. The mast is a two-stage free-lift design with a single hydraulic ram driving a crown sheave at the top of the inner mast. Two parallel leaf chains run over the sheave and tie the carriage to the mast frame, so each chain sees half the load. You need to confirm that BL1034 leaf chain (3×4 lacing, 31.75 mm pitch, catalogue UTS of 222 kN per strand) is adequate, and you want to understand how the chain behaves at light-load, full-load and overload conditions.
Given
- Rated lift capacity = 4,500 lbf (20.0 kN)
- Carriage + forks weight = 1,100 lbf (4.9 kN)
- Number of chain strands = 2 chains
- FUTS per strand (BL1034) = 222 kN
- Safety factor (ANSI B29.8 lift duty) = 5 —
Solution
Step 1 — at nominal full-rated load, calculate the total tensile load seen at the sheave. Because the chain runs over a single sheave with the ram lifting one end and the carriage hanging off the other, each strand sees the full carriage-plus-load weight, not half of it (this is the part that catches new mast designers out — the sheave doubles the ram travel, but each chain still carries the full hanging weight divided only by the number of parallel strands):
Step 2 — calculate the allowable working load per strand using the ANSI B29.8 safety factor of 5:
Step 3 — at nominal, the utilisation ratio is 12.45 / 44.4 = 28%. That is a comfortable margin and is exactly where lift-truck builders aim for, because in real warehouse service the chain sees thousands of cycles a day and you want fatigue life measured in years, not months.
Step 4 — at the low end of the operating range, an unloaded carriage descending under its own weight, only the 4.9 kN carriage hangs on the chain pair, so each strand sees:
At this loading the chain is essentially loafing. Elongation per million cycles is negligible and the dominant wear mode is pin-to-plate sliding at each articulation over the sheave, not tensile fatigue.
Step 5 — at the high end, a careless operator overloading the truck to 6,000 lb (which is what you actually see on the warehouse floor, regardless of the nameplate):
Still inside the 5:1 safety factor, but the cube-law fatigue scaling means strand life drops roughly by a factor of 2 compared to nominal. A chain that would have lasted 8 years in normal service now needs replacement in 4.
Result
BL1034 leaf chain in a two-strand configuration is correctly sized for a 4,500 lb forklift, with each strand running at 28% of its 44. 4 kN working load at full rated capacity. At a no-load descent the chain sees only 5.5% utilisation — practically idling. At a 33% overload condition each strand climbs to 36% of working load, still safe but with measurably shorter fatigue life. If you measure chain elongation faster than expected — say, 2% in two years instead of the typical 0.5% — check three things first: (1) sheave diameter below the recommended 8× pitch, which forces high articulation angles and accelerates pin-plate wear, (2) a misaligned sheave that loads one strand more than the other and causes uneven plate stretch, or (3) corrosion pitting on the pins from washdown chemicals in food-handling environments, which destroys the hardened pin surface and lets articulation wear run away.
When to Use a Block Chain (galle Chain) Drive and When Not To
Leaf chain competes against wire rope and roller chain for lifting and tensile-transmission duty. Each one wins on different axes — load density, wrap radius, fatigue behaviour and inspectability — and the right choice depends on what you are lifting, how far, and how often.
| Property | Block (Leaf) Chain | Wire Rope | Roller Chain |
|---|---|---|---|
| Typical working load per cross-section | Very high — 44 kN on a 31.75 mm pitch BL1034 | High — 40 kN on 13 mm 6×19 IWRC rope | Moderate — 14 kN on ANSI 80 single-strand |
| Minimum sheave/sprocket diameter | 8–12× pitch (smooth sheave) | 16–25× rope diameter | Sprocket sized to tooth count, no minimum diameter rule |
| Maximum operating speed | Low — typically below 0.5 m/s lift speed | Moderate — up to 4 m/s in elevator service | High — sprocket drives run to 1,000+ RPM |
| Retirement criterion | 3% pitch elongation, measured with calipers | Broken wires per lay length, visually counted | 3% pitch elongation or roller wear |
| Failure mode | Plate cracking at pin hole, pin shear | Internal wire fatigue, often hidden until rupture | Roller wear, sprocket tooth hooking |
| Inspection accessibility | Excellent — every plate visible | Poor — internal corrosion is hidden | Excellent — every roller and pin visible |
| Service life in lift duty | 8–15 years typical at 25–30% utilisation | 5–10 years, accelerated by corrosion | Not normally used in pure lift duty |
| Cost per kN of capacity | Moderate — premium over wire rope | Lowest | Highest at high-capacity ratings |
Frequently Asked Questions About Block Chain (galle Chain) Drive
The 5:1 number is specifically for industrial lift trucks under non-personnel duty. The reason it is lower than passenger elevator wire rope (which uses 8:1 or higher) is that leaf chain failure modes are inspectable — you can see every plate and pin from outside the chain — while wire rope hides its broken inner wires until the rope ruptures. The code allows a tighter safety factor because the inspection regime catches degradation earlier.
If you are using leaf chain for a personnel-rated system like a man-lift platform, the safety factor goes up to 8:1 or 10:1 by code, and you reselect a heavier lacing to match.
This is almost always a load-sharing problem, not a chain defect. The most common cause is that the chain anchor adjustments at the dead end were not equalised during the last service — one strand is taking more of the carriage weight than the other, and that strand wears and stretches faster.
Loosen both anchor nuts, lift the carriage to mid-mast, let it hang, and re-tighten so both chains are visibly carrying load with no slack. If the imbalance returns within a few hundred cycles, check the crown sheave — a sheave bearing that has seized or a sheave that has tilted on its shaft will throw the load onto one strand permanently.
No, do not substitute. BL and LH series share pitch dimensions but have different plate thicknesses, different pin diameters and different ultimate tensile strengths. LH chain (heavy series) has thicker plates and larger pins than BL (BL means "British Standard light") at the same pitch and carries roughly 25–40% more load.
The connecting links and end fittings are not interchangeable either. If you replace a BL chain with LH, you also need new clevis ends and the sheave groove width may need to be re-cut. Always match the chain designation stamped on the original side plates.
Start from the working load you need, divide by the catalogue working load of each lacing at your chosen pitch, and pick the lightest lacing that gives you at least a 20% margin over your peak design load. Going heavier than that wastes cost and weight without buying meaningful life.
The other deciding factor is sheave thickness. A 4×4 chain is wider than a 2×3 chain and needs a wider sheave groove and wider mast channels. On a tight retrofit where the mast geometry is fixed, you may have to step up the pitch instead of widening the lacing.
Hole-edge cracking on outer plates at low total cycles points to one of two things: hydrogen embrittlement from improper plating, or shock loading. Cheap aftermarket leaf chain is sometimes electroplated without a post-plating bake, and the trapped hydrogen in the hardened plate causes delayed cracking under tensile load — this is why reputable chain makers either skip the plating or bake at 200°C for 4 hours after.
The shock-load cause is a hydraulic system that lets the carriage drop and snatch on the chain at the end of free-fall, instead of decelerating smoothly. Check the lift cylinder counterbalance valve and the descent control orifice — if the carriage can free-fall more than 25 mm before the chain catches, you are putting impulsive loads on the chain that the static rating does not cover.
Leaf chain wears most where it articulates most. On a forklift mast the chain only flexes at the section that passes over the crown sheave during the lift, so the pins and holes in that section see thousands of articulation cycles per shift while the section above the sheave at full lift just hangs in tension and never bends. The result is highly localised wear.
This is why the inspection procedure says to measure elongation in the most-flexed section, not an average. If that section is over 3% the chain is retired even if the rest still measures fine. Take ten consecutive pitch measurements with calipers in the section that lives over the sheave at typical operating height — that is the section that will fail first.
No. Leaf chain has no rollers and no bushings, so the side plates would slam directly onto the sprocket teeth at every engagement. You would chew through both the chain plates and the sprocket teeth in days. The chain articulates as a smooth bend over a circular sheave — the plates are designed for that geometry only.
If you need a toothed engagement, you need roller chain or silent (inverted-tooth) chain. Pick the chain to suit the drive geometry, not the other way around.
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