Gunstub (3.5e Equipment)
From D&D Wiki
A man with long sleeves is sitting at the bar. You look more closely and see the glint of metal from on of his arms. His entire forearm is replaced with the workings of an iron gun!
This is a graft which a character can acquire on the stub of or in place of a forearm. It functions as the sucket to which an Armgun can be attached and allows the wielding of such weapons.
Because the character no longer has an hand or forearm, the character cannot wield a normal weapon in that hand and cannot bear or wield a shield with that hand or arm. He cannot peform tasks that require two hands (like casting a spell with a somatic component or wielding a weapon in two hands) without using a Sockethand. The character takes a permanent −2 penalty to Dexterity, which cannot be removed by any means except by taking the Gun for an Arm feat.