Jade tips with thicknesses from 0.5 - 20 mm. Jade plugs (blue, blue-black, black-black), also known as FR4 plugs, FR 4 plastic, anti-static FR4 plastic, are plastic made from plastic powder mixed with carbon glass fiber, stone powder, and additives. ...so they are very hard, jade caps are very heat resistant (can withstand 200 degrees for a long time), jade caps are very good insulators, and jade caps are shiny and have very eye-catching colors.