LockNLube LNL134 Grease Fitting Caps, 50 count, Yellow 0.234375 inches,

Fits all standard grease fittings. Appropriate for threading onto 1/4"-28 SAE fittings or M6. For larger fittings, such as 1/8" NPT, the securing strap can be placed over the top of the grease fitting with ample room for the cap to secure as well.