Geezer here, concerning sears for roller-nuts. When I started making crossbows, most of my rollers were made of rock-maple, and fitted with a slotted plate-sear, much like the one shown above. They're surprisingly durable, though occasionally a roller will split along the axis of the plate. The down-side is that they occasionally come adrift and score the nut-socket. And of course, they're a lot of trouble to replace.
Medieval and Renaissance bone rollers usually employed a block-sear, something like a truncated pyramid or wedge, with a little spud on the top that usually shows between the lugs of the nut.
I tried glue-in sears of mild steel round bar... flattened off on the bottom, to take the distal end of the tickler. Those work well enough, if you can get them in straight to begin with. Eventually I hit on using all-thread rod, with a flat and screwdriver slot cut in the bottom. I drill and tap a hole for the threaded sear and simply screw it in place. On rare occasions, I put some glue on the threads, but usually I leave it alone.
Threaded sears can be removed for repair or replacement. Usually I use plain allthread for sears, but Some very strong bows get the stainless allthread. Stainless is harder, more wear-resistant, but of course that means the end of your tickler wears more instead. Generally, repairing a worn trigger is a lot more trouble than replacing a sear.
Now that I have a mortising machine to make life easier, I have considered mortising a square hole in the bottom of the roller-nut and putting in a solid block of steel for a sear. One could drill into the block from the side to mount a set-screw to hold the block in place. So it could be removed for replacement or repair. That would potentially allow a much more substantial sear than is convenient with 5/16 or 3/8 inch allthread that I usually use.
Just thinking out loud. Geezer