The American Rail Adapter Stud HB6A is for for American size rails, 5/16" across the rail slot.

Note about our photos:
While we make every effort to ensure that our product photos are accurate, manufacturers occasionally change the design of components such as triggers, sights, or magazines without notice. Also, modifications to the firearm or component may be required in order to meet specific state compliance requirements. While we make every effort to accurately describe and illustrate the item you are going to receive, there may be visual differences on various components that do not affect functionality.