Singer 27 screw center with nut.  For arm rocker shaft.  Lower screw center #301A with nut #1508C. May work on other Singer machines. Measures 1/2" diameter x 1 1/16" (tip to base). With Singer threading (luck figurin' them out). Nut is 11/16" diameter w/1/2" hole.  $4 shipping to lower 48.