Battle Arms Development, Inc. Pdw Stock System, Black Finish, Complete With Stock Assembly, Ultra Compact Buffer System And Springs, No Proprietary Bolt Carrier Required, Not Compatible With Lowers That Have Built-in Qd Attachments, Will Not Work With Solid Filled 9mm Bolt Carries, Will Not Work With Solid Filled 9mm Bolt Carrieiameter X .625" Deep Minimum To Clear The Buffer Bad-css