Delrin is a brand name of acetal plastic, and comes in several formulations. AF has teflon impregnation to make it more slippery (and also more costly...). For that app I would use UHMWPE. It should be cheaper and as others have said as less water absorption. Doesn't machine nearly as nicely though. The high priced option would be PEEK, but the material will be at least 10 times as expensive.