Luth-AR Grovtec Threaded Base/Cup Black. The GrovTec base cup can be threaded into the side cup holes on all MBA buttstocks (MBA-1 MBA-2 MBA-3 and MBA-4). Each buttstock has a side cup hole on both sides of the buttstock frame. The cup can be installed with an separately available installation tool or a 1/4? Allen wrench. Specifications for Luth-AR Grovtec Base/Cup: Manufacturer: Luth-AR Color: Black Features of Luth-AR Grovtec Base/Cup: Shipping Weight .2 lbs Shipping Dimensions 1 x 1 x 1 in Package Contents: Luth-AR Grovtec Base/Cup Luth-AR GT-CUP: Grovtec Threaded Base/Cup Black