User blog comment:B214/Question and Answers 2/@comment-4547267-20140604230500/@comment-1359322-20140605094434

If Issei loses both his arm, then he won't be able to use his Boosted Gear. For Sacred Gears with forms like the BG where the Gear is part of the body, their body part is important. This is like a holder-type SG, a body-type SG, and a bodyless type SG.

Holder SG are Sacred Gears like True Longinus, where the SG materializes outside the possessors body.

Body SG are Sacred Gears like Boosted Gear, Divine Dividing, Absorption Line and Forbidden Balor View. That type of Sacred Gear require the specific body part to activate, losing it would mean losing the ability to summon the Gear. Like if Gasper's eyes are crushed, then he wouldn't be able to stop time anymore.

Bodyless SG are Sacred Gears like Sword Birth, Blade Blacksmith, Annihilation Maker. They don't have a form, it's powers are placed inside the possessors' body and can restore many times over. Like Kiba's Sword Birth, the swords can be broken time and time again, but Kiba can create more.