The grease fitting is used in a bearing.
uxcell Brass Straight Grease Fitting Assortment M8 x 1mm Thread Hydraulic Grease
uxcell Brass Straight Grease Fitting M4 x 0.7mm Thread x 0.7mm, Yellow
uxcell Brass Straight Grease Fitting M6 x 0.75mm Thread x 0.75mm, Yellow