Titanium Threadless with Hexagon Top comes in 4mm and fits into any Invictus threadless barbell or base. Manufactured from High Polish Implant Grade Titanium (Ti-6AL-4V-ELI ASTM F136). To secure the inside bar or base, add a slight bend to the pin by simply inserting the pin half way and pushing the top to one side. Pin Size: 0.45mm x 4.7mm. Material sourced in the USA.