The grease fitting is designed for use in a bearing.
uxcell Steel Straight Grease Fitting M8 x 1mm Thread x 1mm, Silver Tone
uxcell Steel Straight Grease Fitting M6 x 1mm Thread x 1mm, Silver Tone
uxcell 304 Stainless Steel Straight Grease Fitting M6 x 1mm x 1mm, Silver