Bob,

I had crotch belts custom made up for me several years ago and added them to my existing four point belts.  For me this was to keep me in my seat in turbulence and aerobatics, not crash worthiness, so I did not engineer the attach point for crash loads.  One could do that I suppose.

I still have a few of them (had a minimum order requirement).

Attached are installed pictures.  The crotch belt end is long and slotted and fits over the end of the male lap belt fitting, just like the shoulder belts.  The shoulder belt ends have a left and right angle at the belt end, while the crotch end is straight.  Unfortunately, I don't have any pictures of these ends handy, but I can take some if you need.

I fabricated an aluminum bracket to bolt the crotch belt to the floor and glassed that in.  You can see the size of the patch in pale green.  Can't remember the bid schedule, but it was probably four or five.

I then cut a slot in the seat pan for the crotch belt to come up top.

Tom Thibault
LNC2, N4XB, "Eagle Dancer"