if it's going into a t-tube: a)make sure you didn't tape your stocks in the t tube to hold them in place temporarily because it leaves sticky crap everywhere that's hard to get off, and b)I don't know if you can find or order anything that is less than a quarter of a millimeter smaller than 7/8" diameter, but if you can, do so, because otherwise you'll have to do what I did and sand down the inside of your t-tube top so that it will fit in, because stocks are slightly smaller than 7/8" to my knowledge..