Installing a Holosun HS407k-x2 on a sig p365x?

I have 500+ rounds through my P365x with HS 407k since install. It went pretty much as expected. From an install tool point of view, I used:

• Hex 5/64" allen key (to remove Sig Iron Sight screws)
• Hex 5/64" insert in my Craftsman hex driver (ditto)
• Sharpie (apply torque stripe)
• Torx T-handle T-10 driver (to start Holosun screws)
• Wheeler FAT Wrench with a Wiha T10 insert set at 15 in lbs (final torque of Holosun screws)

I used the smaller of the two Holosun screws that came in the package. I "believe" these are M3-0.5mm pitch, approx 1/2". I opted to leave the dry blue threadlocker on the holosun screws and installed normally. I started them with the T10 driver, to make sure they were not cross threaded, then used my FAT wrench at 15 in lbs.

RolexGMT said:

Does anyone know if you use the wrench that comes with the holosun 407k-x2 to install the red dot? I know it sounds like a stupid question but better to be safe than sorry!!! I read in the sig manual to use a 5/64 hex and then learned out the 2mm was a better fit and should use that???

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Forgive me but I think you may be confusing the two screws.

First, the sight cover plate is attached to the slide with a 5/64" / 2mm allen head hex screw. The reason I say 5/64" / 2 mm is that these are almost identical. 5/64 is 0.078125". 2 mm is 0,078740", just ever so slightly larger.

Given typical manufacturing tolerances on these small screws, you are going to find a sample to sample variation. I would try both 5/64", and 2 mm Allen wrenches. Use which ever one gives you the best fit, on your particular slide cover plate screws.

Beware: Allen keys are notoriously easy to strip. FIRM STEADY PRESSURE is all you want. DO NOT FORCE the screw. If you are comfortable with putting on localized heat, use a small (very small) pencil soldering iron, and gently (GENTLY!) add heat to the screw head. DO NOT OVERHEAT. At some point the steady force will allow the screw to be removed.


Now, let's turn to the sight body. It is held onto the slide with two Torx T-10 screws. These are supplied by Holosun.

The tool that comes with the Holosun has two ends, one small flat blade for the battery tray screw (and to lever out the battery tray; check the manual) and a Torx T-10 bit for the screws.

Can you use the T-10 side to install the sight? Yes, you can. But:

Unless your fingers are calibrated, one cannot reliably install the screws to the torque specified by Holosun (15 in lbs).

If you aren't comfortable working in inch pounds, or do not possess a calibrated torque wrench, or have long experience in installing small-torque fittings, I would STOP HERE AND SEEK OUT A GUNSMITH. For sure, install the sight with the tool, snug it down, but get someone with a real torque wrench to apply final torque before you shoot it.

There are many options for torque wrenches in in lbs, but if you are doing just this one, it would be worth just getting someone to do it for you. If you were near me, I'd tighten it for you. I opted to buy a Wheeler FAT Wrench, and a Wiha T-10 bit to do mine, but it was worth it for me as I've done 6 or 7 installs now.

On threadlocker, I have found following Holosun's advice to use blue/medium on the screws to work well. They apply some from the factory, so you may find it on the screws, already. If so, you can screw them in place with out additional threadlocker. I use a bottle of blue, but many folks find that the Loctite Blue "stick" type works well since it won't drip.

Lastly use some kind of torque striping. This is just a fancy way of saying paint the screw head with something (white nail polish, sharpie, paint stick, etc.) so that if the screw moves, you will have a way to notice it. Make a practice of examing the witness marks at the range before you start shooting, and retorque if necessary.

Good luck!