Ken, no the MP40 has a M13x1 metric thread.

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/

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=

No, the gsg mp40 has a weird thread pitch of M13×1. You would need a M13×1 to 1/2×28 thread adapter Wich is honestly your best option because like I said m13×1 isn't very common and not alot of options available with that thread pitch. Hope this helps.