This is a AR picatinny foregrip w/ tactical light.
Activate the light at will with a single touch of the thumb on the grip.
NOTE:This model requires the MAGLITE LED XL50 FLASHLIGHT. It is a little pricey but bright as the surface of the sun. Get it at Amazon.com
The upper fits into the lower very snug, you should not need to sand them- Use a rubber mallet to gently force the two together. Glue if you want to, I don't.
Use 4-40 screw and nut to hold upper and lower together.
When placing the light in the upper there will likely be a little sanding necessary, you want a snug fit but not jammed.
Put the push button in first, slide the light back until it just barely touches, then use two 4-40 screws and nuts to clamp down the light.
Use two 6-32 nuts and bolts to hold the grip to the rail.
You should be able to get all nuts and bolts at the box hardware store of your choice.
If you need to, use a Dremel cut off tool to trim the bolts.