This insert is made for a feed slot cut: 147.6mm ( 5 13/16" = 5.8") long and 12mm wide.
Inside channel diameter = 14.73mm
Bottom nipples have a small hole to mark the drilling location inside the feed slot for 3/16" holes.
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Surface texture of nylon can be dyed a color. Black is best of UV protection.
File 7/11/22 better Catalina 22 Sport-TD=17.119mm.pg352A.v.301