The grease fitting is used in a bearing.
uxcell 304 Stainless Steel Straight Grease Fitting M10 x x 1mm, Silver
uxcell 304 Stainless Steel Straight Grease Fitting M6 x 1mm Thread x
uxcell 304 Stainless Steel Straight Grease Fitting M10 x 1mm Thread x
uxcell Brass Straight Grease Fitting M5 x 0.8mm Thread x 0.8mm, Yellow
uxcell Brass Straight Grease Fitting M4 x 0.7mm Thread x 0.7mm, Yellow