This is the same inlay that is used at JCS Musical Instruments.

Guitar inlay side dot marker. Condition is new. Shipped with USPS In Standard envelope. 1/16” White Plastic Side Dot Material 9 pieces, 7 inch rods for musical instruments. Common on Fender necks at side of fret boards. Plastic dowel rods for making position dot markers on the edge of the neck. Size: 1/16" inch (1.58 mm) diameter ROD. Requires a 1/16” drill bit at .0625” diameter for best fit. BUILDERS NOTE: I Drill a hole 1/4" deep that is slip fit and then lightly glue in each one with water thin or medium CA (Super Glue). Cut and scrape or file the material flush after insertion.