This Nerf gun laser sight mount is designed for cheap keychain lasers. You'll need to provide four screws--one to activate the power button, and three to align the laser. You can customize it with whatever dimensions you want.
The cheap keychain lasers definitely require the adjustment screws: the beam can be off as much as 8 inches at 6 feet away!
You can align using my collimator collimator: just put the laser in the sight mount, and rotate the mount upside down in the vee-shaped holes of the collimator collimator, while shining it at something a couple of meters away. Then adjust the adjustment screws until the spot doesn't move much when rotating (up to you how precise you dial it in).