A helmet accessory attachment member includes a finger-actuatable lock configured to secure an accessory attachment member mount to a helmet mount as part of securing an accessory such as a mandible guard to a helmet. The lock includes a pivot arm with a rotation axis that is parallel to the helmet surface, and also includes one or more blocking surfaces on the pivot arm to engage with grooves on the helmet mount. The lock may be positioned on a slidable insert of the accessory attachment member.