3.25" Nitrile Butadiene Rubber (NBR) Cover. This short foam rubber cover will fit on every tube we carry, Receiver Extension Tubes (RET) or Pistol Buffer Tubes (PBT). This material is spongy, durable, washable, and lets you get a comfortable cheek weld. The exterior surface is smooth, so it's easily cleaned off after a long day at the range pressing your greasy mug up against it. This is a physically thicker material than our other covers, so we offer it in this shorter length to allow room for charging handle operation.
Photo shows foam cover on an Entry Length Receiver Extension Tube