This is the one you want for a geissele mk4 - Arisaka Defense Inline Scout M-LOK Mounts

Arisaka makes solid, solid stuff. We can get that out of the way first. If you get a mount from them that doesn't suit you it's all about your application, not the quality of the mount.

That said, this is the mount you want for a scout light on a Geissle MK4 rail, or a similar with MLOK slots at the 45-degree position. It tucks your light in at about the 2 o'clock position and for me, it's perfect. All our Lego guns are different :) but if you're looking for an inline mount, this is a great option. One note if using this on the Streamlight HL-X, because of the length of the light body the front-most mounting screw isn't accessible with a regular hex key. Simple solution: Take one and just chop it off short. It'll take you a few minutes to get it screwed down but the end result is worth it.