Ive used them form all kinds of stuff I end up collecting. Sometimes ya need a stud mount and sometimes ya have room for a couple tabs to get tacked on.
I would go to the wrecking yard and wander around till I seen the perfect one for my application. At the same time making note of other good parts I see along the way.
I've heard of a lot of guys using pathfinder bumps.
I get these from a local tire shop for a couple of bucks a piece. Single stud mount, not progressive obviously or real soft, but they're pretty handy.
Did those come with the round stock??? What the length???
Here are the ones I use, they are off a 1990s Chev 4x4 rear. 3"x3"x2" solid rubber. Alot of the race jeeps use them too. This set came from Billybobs