Combat Armory Thread Protector 9/16 x 24 (.40&10mm) 16X24 The Combat Armory thread protector is manufactured from solid 303 stainless steel. Designed to protect your threaded barrel when an accessory is not installed. This thread protector is common to 40 caliber threaded barrels. (including 10mm threaded barrels) Fits all 9/16 x 24 threaded barrels.