D-nail - Optech Mushroom Valve (Clear Sapphire)Dnail
They are designed to work as valves for slurpers, but happen to work great upside down in 16-20mm blenders.
Total Height: 32mm
Upper diameter: 10mm (fits most slurpers)
Stem: 22mm deep, 4mm min 6mm max diameter, concave.
The curvature of this shape affords a guide for the oil, with the narrowest part of the stem being a low-pressure zone comparatively. This helps mitigate splash and control where to focus your heat, knowing where the oil will spend the most time.