Field and Sons Leg irons

I have just got Field and Sons leg irons, but without a key. Hiatt keys won't fit. Is there a way to measure the TPI of the bolt, and the diameter, with everyday tools, so a key can be ordered?

I managed to measure the pitch of the internal threaded bolt by making an impression with playdo on a wire. The average of 10 measurements was 11.1 TPI, with a standard deviation of 0.13. In comparison, Hiatt Leg irons appeared to be 10 TPI. To find the thread diameter, I drilled out a plastic rod until it just slid over the threads. Outer diameter of the threaded bolt was 0.290".

I have just got Field and Sons leg irons, but without a key. Hiatt keys won't fit. Is there a way to measure the TPI of the bolt, and the diameter, with everyday tools, so a key can be ordered?

Leg iron keys are a pain. I have found that they are not all alike even with one manufacturer. Plus the springs are often very strong which means they can be difficult to open even with a perfect key.

One of the best tools I own is a special Cruciform Key beautifully designed and made by Ian McColl. It is like the one that the Cannon's sell for handcuffs, but somewhat bigger. Not only does it grip the bolt in most any Darby leg iron, the handle give you the necessary leverage to open the thing.

Joe

I have just got Field and Sons leg irons, but without a key. Hiatt keys won't fit. Is there a way to measure the TPI of the bolt, and the diameter, with everyday tools, so a key can be ordered?

I finally determined the key measurements for these shackles are as follows:

Bolt major diameter 0.280” (measured from a photograph)
Bolt minor diameter 0.240” (measured from a photograph)
Shoulder-to-bolt depth 0.63” (measured with depth gauge)
Keyhole diameter 0.38” (measured with calipers)
Bolt thread 11 TPI right hand thread (measured with Playdo impression)

Ian made me a key to these measurements, and it worked perfectly.