The Triumph Twist Drill Co. 5/16-Inch Jobber Length Fractional Drill Bit is a precision-ground jobber-length twist drill from Triumph Twist Drill Co., sized to a true .3125-inch fractional diameter for gunsmiths and hobby machinists who need an exact bore for pin holes, dowel holes, or sight and scope-mount work on the bench. It follows the standard machinist sizing system gunsmiths rely on when working from a published drill-and-tap schedule. Jobber length keeps the flutes long enough for through-drilling typical receiver, barrel, and stock material without extra reach. It’s a straightforward, no-frills addition to any gunsmithing drill index.

Key Specifications

• Ground to a true .3125-inch fractional diameter, the confirmed bore size for this bit.
• Sized under the 5/16-inch fractional system, matching standard fractional drill schedules.
• Machined to jobber length, the standard flute length for bench and drill-press through-holes.

Frequently Asked Questions

What is the actual diameter of this bit? It measures a true .3125-inch fractional diameter, per the manufacturer’s drill sizing chart.

Is this a jobber-length bit? Yes, it’s ground to standard jobber length, the flute length most gunsmithing bench and drill-press work calls for.

Buy the Triumph Twist Drill Co. 5/16-Inch Jobber Length Fractional Drill Bit

Keep a complete, accurately sized drill index on the bench instead of forcing an ill-fitting bit into a job. Order it from our gunsmithing tools and supplies selection for fast shipping direct to your door.