BenchReference / Drill sizes / T T Drill Bit Decimal inches 0.3580″
Millimeters 9.093 mm
System Letter
Nearest equivalents in other systems System Nearest drill Size Difference Metric 9.1 mm 0.3583″ / 9.1 mm +0.007 mm (+0.0003″)
Fractional inch 23/64″ 0.3594″ / 9.128 mm +0.035 mm (+0.0014″)
Number (wire gauge) #1 0.2280″ / 5.791 mm −3.302 mm (−0.1300″)
−0.727 mm +0.727 mm T R −0.483 mm S −0.254 mm U +0.254 mm V +0.483 mm 9.1 mm +0.007 mm 23/64″ +0.035 mm ← #1 −3.302 mm tick position = true diameter · letter neighbors above, equivalents below · window ±0.73 mm
Positive difference = cuts a slightly larger hole than T. Sizes
beyond the window are listed with arrows — they are not close substitutes.
Neighboring letter sizes Drill Decimal in mm vs T R 0.3390 8.611 −0.483 mm S 0.3480 8.839 −0.254 mm T 0.3580 9.093 — U 0.3680 9.347 +0.254 mm V 0.3770 9.576 +0.483 mm
← S (smaller) U (larger) →
Compare T 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 0.3580″. See all data sources .