I'm not sure if you have this option but I'll explain how I do it. I start the front side of the slats up on the front hubs and stick a pry bar though the slats against my axle and then use the backside of my upright portion of my frame to wedge my prybar behind to keep it from rolling off the hubs. Then bring the back half of the slats on around from the backside of the mill and use a 1/8" bar to stick between your slats to have something to clamp against while you tie your two ends together. To tie them together I split the difference in my connecting slat and bolt each side of the slat to the belt. Then I take a strip of belt that will cover three slats and bolt it to the inside of my original connection to reinforce the joint. I hope that makes sense or at least gives you ideas of a different option than what your looking for. I think what you may be describing is what we use to connect hay Bailer belts. It's like a key way that you bring together that has the little eyes built in it that interlock, then you slide the locking wire through them to tie it in? If so you can by them at any John Deere or new holland type store that sales tractors or hay bailers.