Midwest Industries Polymer M-LOK Rail, Fits M-LOK Handguards, 3 Slot, Polymer Construction, Matte Finish, Black, Hardware Included MI-3PMR Midwest Industries Polymer Picatinny Rail will fit standard M-LOK Slots. Midwest Industries is a proven leader in the firearm industry. Made in the USA" focusing on the small details to make your rifle platform better. The addition of their rail sections to your rifle platform creates the rail space you need to add accessories.