10 pc wheels have 19mm outside diameter, 0.5mm thick. Diamond Coated for Extra Strength and Long Life of Blades. Breathing Holes for Heat Reduction and removal of debris. Includes 1/8" (3.175mm) Mandrel. Compatible with Dremel, Foredom and other Rotary Tools. US-BASED CUSTOMER SERVICE: Available by chat, email, phone, or visit us at our customer service center in La Crosse, WI.