Replacement zinc plated boat trailer roller shaft pal nut. These will fit onto the end of a 1/2" Roller shaft and are used to keep your roller shaft in place and the roller secure. These 1/2 inch Roller caps are easiest to install with the roller and bracket assembly off the trailer. You would want to hammer on one side securely, then put the roller shaft and roller in place inside the bracket. Next, you will want to rest the already mounted end against a secure surface to provide the resistance needed to hammer on the other Pal Nut. You can use these 1/2 inch pal nuts with both stainless steel and zinc plated roller shafts of the same diameter. Additionally keep in mind that when using stainless steel roller shafts you will want file or score the ends of the shafts where the Pal Nut would bite. You want a rough surface on the stainless steel for a solid grip.