Flangeless Plug for M20 Screw Holes, Ød18mm to ØD20mm, 25.4mm Long, Silicone (Blue), Pack of 10, HBFS200-P
SGD $29.70
Every flangeless plug is conical and hollow for a flexible fit. Furthermore, they have a knob for easy installation and removal. The threaded profile prevents excess paint from adhering to screw holes.