Size probably depends on your type of mast. My 2003 H260 has a US Spars mast. The slugs that fit are by Bainbridge A018S 7/16". I've broken several slugs so order a dozen. Readily available on many websites. There are two types, the plastic and SS bale. Shop around. I think I paid a lot less than what is offered on the WM site but can't find my invoice.