O-ring strap bumpers are made of rubber and are thicker than the other bumpers. It's also recommended to use them if you are attaching your strap to a rod. This will keep the split ring securely in place. They're also easily added after the strap has been assembled. $1 each.
Octagonal strap bumpers are a great leather option and can be added to your camera at any time. Although we make them thinner, the same leather is used as the straps and they're available in the same colors. $4 each.
Integral Strap Bumpers are assembled in the loop of the strap. They can then be placed between the lug-mount and the split ring for protection. We thin the same leather that's used for the straps so the same colors are available. Because the strap is assembled together with the Integral strap bumper they can not be added after the strap has been assembled. $4 each.