Made from Heat treated 410 Stainless Steel for Ultimate Durability. – No Spacer is required for 9mm/.38 magazines. – 126mm 9mm/.38 magazines hold 20-21 rounds. – 126mm .40/10mm magazines hold 18-19 rounds. – 141.25mm 9mm/.38 magazines hold 23-24 rounds. – 141.25mm .40 Cal/10mm magazines hold 20-21 rounds. – 155mm 9mm/.38 magazines hold 27 rounds. – 171.25mm 9mm/.38 magazines hold 29-30 rounds. – 171.25mm .40 Cal/10mm magazines hold 26 rounds – Made with Exclusive Features to meet the Highest Demands for today’s Shooters. – Witness holes on the rear of the tube to indicate round count. – MBX Tube is designed to work with sti/sv & all 2011 style pistol grips and mag catch heights. However, the NEW sti grips due to the reworking on some models, MBX cannot guarantee our magazines will drop-free and the grip may need to be adjusted. – MBX Tubes are designed to work exclusively with MBX Springs, Followers, & Basepad. MBX Tubes are not designed to work with other manufacturers components. MBX Magazines are Made to Work Right out of the Bag!