BenchReference / Drill sizes / S S Drill Bit Decimal inches 0.3480″
Millimeters 8.839 mm
System Letter
Nearest equivalents in other systems System Nearest drill Size Difference Metric 8.8 mm 0.3465″ / 8.8 mm −0.039 mm (−0.0015″)
Fractional inch 11/32″ 0.3438″ / 8.731 mm −0.108 mm (−0.0042″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −3.048 mm (−0.1200″)
−0.707 mm +0.707 mm S Q −0.406 mm R −0.229 mm T +0.254 mm U +0.508 mm 11/32″ −0.108 mm 8.8 mm −0.039 mm ← #1 −3.048 mm tick position = true diameter · letter neighbors above, equivalents below · window ±0.71 mm
Positive difference = cuts a slightly larger hole than S. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring letter sizes Drill Decimal in mm vs S Q 0.3320 8.433 −0.406 mm R 0.3390 8.611 −0.229 mm S 0.3480 8.839 — T 0.3580 9.093 +0.254 mm U 0.3680 9.347 +0.508 mm
← R (smaller) T (larger) →
Compare S with another size
Data provenance. ASME B94.11M, Twist Drills (standard drill size series) (ASME). Millimeter and inch values are converted with the exact definition 1 in = 25.4 mm; the canonical dimension for this letter size is 0.3480″. See all data sources .