What 870 do you have that a Simms (R3 in the Rem catalogs) is not made for? Every 870 we have had from the factory has been ordered with them if they didn't come as standard equipment. I have replaced pads on nearly a dozen of my long guns and my only choices are the Simms/R3s or the Pachmayer Declerator. They are AWESOME pads. I put a slip on on my 835 turkey gun lastyear after I dug it back out (hadn't used it since the 870Supermags came out several years ago) and it REALLY make a difference on that heavy hitter (2.25oz of 4x5x7 Nitro Hevi-Shot). I picked the slip on because the gun is fugly to begin with (old Real Tree camo) and I wanted to increase the length of pull so I put it on over the factory pad.

I LOVE the Simms pads, even my kids guns have them on as well.
RA