It has M13x1 threads, they make adapters for other thread pitches like more popular 1/2×28 threads. Hope this helps.

Ken, the GSG MP40's M13x1 thread pitch would need this adapter to work with the 1/2x28 Flash Hider : -- downrangeproductsco.com/product-category/barrel-thread-adapters/m13-5-x-1-lh-to-1-2-x-28-barrel-thread-adapters/

Ken, no the MP40 has a M13x1 metric thread.

No this has a European M13x1 metric thread, according to ATI's website they are the company that imports these for GSG from germany.Germany. They make an adapter to convert the threading to a standard 9mm barrel threading of ½x28 ( like what you linked to) they also have an adapter to co vertical to ½x36. Both out of stock right now at buds, but hit the notify me when available button to receive an email when they come back in stock. budsgunshop.com/search.php?q=819644020332&type=