IBLS Coupler and Safety Chain Standards

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Coupler, Chain and Hook Arrangement

Coupler and Safety Chain Arrangement
Scale Gauge Coupler/Chain Hook Height (CH) Chain Offset (CO) Hook Size Link SizeChain Length
1/2" 2-1/2" 1-15/16
3/4" 3-1/2" 2-1/4
1" 4-3/4" 2-7/8" +/- 1/4" 1-1/4" 0.11" 3-1/2" +/- 1/2"
1" 5" 3-1/4" +/- 1/4" 1-1/4" 0.11" 3-1/2" +/- 1/2"
1-1/2" 7-1/4" 4-7/16" +0" -3/16" 2-1/2" +/- 1/4" 1/4" 1/8"x1" welded7" +/- 1"
1-1/2" 7-1/2" 4-7/16" +0" -3/16" 2-1/2" +/- 1/4" 1/4" 1/8"x1" welded 7" +/- 1"
1.6" 7-1/2" 4-7/16" +0 -3/16" 2-1/2" +/- 1/4" 1/4" 1/8"x1" welded 7" +/- 1"
2.5" 7-1/4"+ 5.4"
3" 12" 7.5"
  • Explanation
    • Coupler height is measured from the top of rail to the horizontal center-line of the coupler
    • Right hook is a captive hook
    • Left hook is an open hook
    • Hook Size refers to the diameter of the hook shank
    • Chains must pass over hooks
    • When chain is not in use it should be hooked onto the open hook of the same car
      • 2013/03/20 - Added 1" length to chains for 1-1/2" and 1.6" scale to provide enough length when not in use
    • If cars are close due to short coupler shanks the 2nd or 3rd link from the end of the chain can be hooked onto the open hook of the other car.
Safety chains and hooks in end-sill.
From DiscoverLiveSteam.com

Tidbits From Chaski

From http://www.chaski.com/homemachinist

Carl B "ccvstmr"

ILS standard calls for two (2) 1/4" hooks at 2.5" distance from the centerline of the car. I set the hooks at 3" because I don't like to "crowd" the coupler. Eyebolts with 1/4x20 thread and various length shanks can be purchased at most hardware stores. The left hook is twisted open while the right hook is opened...the chain inserted...and the hook closed to make the chain captive. I would suggest putting hooks in a vise and using a crescent wrench to twist the hook open as much as needed to slip the chain on...and then close the eye bolt. Do not try to "unwind" the the hook loop and then squeeze it closed.
Example application of safety chains and hooks
Chains are 6" +/- 1". Chain material is 1/8" x 1" welded link...although 3/16" x 1" link would also do. The chain must fit over the chain hooks. Wire-wrap chain is not acceptable either.
One point that is often overlooked...is the method in which the the chain hooks are attached to the loco/car body. A screw-in eye-bolt hook is not acceptable, nor is a hook attached to an end-sill that is nailed to the end of the car. In other words, the hook attachment to the car body must be strong enough to withstand the forces transmitted through the chain(s) during a derailment. It is better to destroy the hook (straighten it out) instead of destroying your rolling stock or let your cars get away and be stopped by the next train that follows.
If anchoring hook in metal...drill a #7 hole and tap for a 1/4-20 thread. Use a nut on both sides to "lock" the eye bolt in place. If anchoring hook in wood...drill a 1/4" hole and again, use a nut on the face and back to hold in place. Do not use "lag" type eye bolts for wood. If you have a wood end sill...back it up with a well anchored piece of steel angle. If the equipment uncouples, you don't want the chains to yank the wooden sill off. btw...flange nuts look decent on the face...Nylok nuts on the back.
Another item to watch for...always make sure that safety chains are hooked at both ends...even if it's the last car of the train. A dragging chain will easily catch a turnout frog and/or heel block if you're not careful. The result...time to replace the chain hooks. Hope this helps.
Coupler height...most clubs have coupler height specs. Some follow IBLS, others are not far away. Usually the center of the coupler is set 4-1/4" to 4-7/16" over the rail head. Of course, as long as "out of spec" equipment is not coupled or run with "in spec" equipment, there's no problem. However, if the couplers have excess vertical motion, this is where a problem can start.
Quick Link Chain Repair


At Train Mountain they do it much as described above, but they use closed eyes and threaded chain "repair links" (you know the ones).

10 Wheeler Rob

Purpose of safety chains is not for derailments, but to keep rolling stock and a cargo of pasengers from rolling away in the event of a coupler failure or disconect. This is because very few cars have self energized brakes in the hobby.

cvstrr writes:

Lee Wright safety chains
Depending on the design of the underside of the rolling stock, you could follow something along the line of what Lee Wright does. Lee either welds a chain tab on the underside of the car or drills a hole in the flange of his centersill. "D" rings are used to connect the chain to the tab or centersill flange. The chain is 1/8" links about 1" long. While this may not be exactly on the centerline of the car, it's still pretty darn close.
One possible drawback (there's always a tradeoff), you have to get down on the ground to find the hole or D ring to connect the chains. The photo shows two chains, but you could probably get away with one.