TLR-1 Crossbolt

Hello all. I'm replacing five screws on a TLR-1 HL with Ti. There's three with 4-40 and one with 6-32 threads. The crossbolt that tightens it to the rail is s mystery to me. It's a. It smaller than 8-32 and seems to have metric dimensions of M4x.8, but that's not a standard fastener size. Streamlight customer service said they could send me a new bolt, but didn't know the thread dimensions. Obviously I could use a number of different size fasteners to get the job done, but I'd like to use the factory tapped threads. Thanks!