This is a Magpul Industries Accessory known as the Cheek Riser MOE/CTR, model MAG325-BLK.
Clip on cheek riser for the MOE and CTR stocks. Raises cheek weld 1/4 inch in height. This riser is for use on NON AR15/M4 applications as the riser will interfere with charging handle function. Originally designed for M14 carbine stock conversions.
Features:
Originally designed for M14 carbine stock conversions