HO Train Coupler Lock

Hello all HO train modelers,
I am just beginning the HO train hobby with my son and as such we are starting out with some pretty cheap parts and cars. We have been having a problem with the knuckle couplers detaching, especially when my son is not being the most gentle :) So this lock fits around the two knuckle couplers after they are attached.

I used a small rubberband (like my kids use with band looms) to give the clamping lock a nice easy snap into position. The knuckles should be link