Never clamp oversized tool shanks. For example, never use a Ø 12 mm to 11 mm collet to clamp a Ø 12.2 mm shank. Rather use the next bigger collet (in this case a Ø 12.5 mm – 11.5 mm or 13 mm – 12 mm collet). Insert tool to the full length of the collet for best results if possible. Also, never insert the tool less than 2/3 of the collet length.