Can someone tell me what size the hex keys are for the M&P22 front and rear sight. I can't find the ones that came with the gun and don't have any at home. Thanks.

It takes a decent quality 1/16" allen wrench.

So both the front and rear the same size?

Update - found the answer on another forum. The front sight uses a .050 hex key.

1/16 is too large for my M&P22 - the best fit I've found is a 1.3 mm hex, the next best (a bit loose) is a 0.05" SAE hex. You can order a 1.3 hex with handle from Amazon for typically less than $4. The one they provide with the gun is too easy to lose.