Unfortunately Streamlight does not provide the size of the hex wrench, however the size you need is included with the TLR-6.
Metric 1.3 is the right size (just used it on mine). If all you have is sae .050 it would work. It’s just not quite as snug and you run the risk of stripping out the screw.
Standard metric hex-keys in this range are 0.9mm, 1.3mm, and 1.5mm. All are typically included in a standard folding set for about $10. A set of two SAE/ metric are often sold together and make a great gift for any shooter or gear-head. A low-cost vernier caliper measures the hex-key included with my TLR-6 at very close to 1.3mm.
It’s an SAE .05. You can buy a Husky mini Allen key set at Home Depot. The .05 is the size smaller than the 1/16th
This works. Dynamite Machined Hex Driver, Red: .050", DYN2910
CR-V T-6 Which is very small
Mini T5 torx screw head worked for me. Be very gentle and apply constant pressure to adjust to avoid stripping. Frankly one of the weakest points about this otherwise super solid product.