Spanner Size Chart (Metric-Imperial Equivalents)

For your convenience, we’ve compiled a simplified chart of which spanner to use for each size of bolt or nut.

Are spanners and wrenches the same?

They essentially have the same purpose: to tighten and loosen nuts and bolts. Nevertheless, they have distinct characteristics designed for specific use cases. 

Put simply: 

  • Spanners have slimmer, fixed-sized heads that are designed to drive nuts and bolts of specific sizes. 
  • Wrenches have a thicker “head" with an adjustable/movable lower “jaw” and are designed to drive nuts and bolts of a range of sizes. Being adjustable, you can virtually use them on any bolt the head and jaw can clamp onto. 

Shop for spanners and wrenches. 

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Metric vs Imperial equivalents 

Refer to this table when referencing which spanner size to use for your bolt, nut or screw with a hexagonal head. 

METRIC IMPERIAL UNC/UNF
Spanner Size (mm) Spanner Size (inches)
Metric threads Alternative sizing Class 4.6/8.8 Structural Stainless SAE Decimal Inches Grade 5/8 AF
    AS 1111 AS 1252 DIN 931 / 933 / 934     AS 2465
M 1.6 --- 3.20 --- 3.20 --- --- ---
M 2.0 --- 4.00 --- 4.00 --- --- ---
M 2.5 --- 5.00 --- 5.00 --- --- ---
M 3.0 --- 5.50 --- 5.50 --- --- ---
--- 3.18 --- --- --- 1/8 0.125 ---
M 4.0 --- 7.00 --- 7.00 5/32 0.156 ---
--- 4.76 --- --- --- 3/16 0.188 ---
M 5.0 --- 8.00 --- 8.00 3/16 0.188 ---
--- 5.56 --- --- --- 7/32 0.218 ---
M 6.0 6.35 10.00 --- 10.00 1/4 0.250 7/16
M 7.0 --- 11.00 --- 11.00 --- 0.267 ---
--- 7.14 --- --- --- 9/32 0.281 ---
M 8.0 --- 13.00 --- 13.00 5/16 0.313 1/2
--- --- --- --- --- 11/32 0.343 ---
M 9.0 9.50 --- --- --- 3/8 0.375 9/16
M 10.0 --- 16.00 --- 17.00 3/8 0.375 9/16
M 11.0 --- --- --- --- 7/16 0.438 5/8
M 12.0 --- 18.00 21.00 19.00 1/2 0.500 3/4
--- 12.70 --- --- --- 1/2 0.500 3/4
M 13.0 --- --- --- --- 1/2 0.500 3/4
M 14.0 14.30 21.00 --- 22.00 9/16 0.563 13/16
M 15.0 --- --- --- --- 9/16 0.563 13/16
M 16.0 --- 24.00 27.00 24.00 5/8 0.625 15/16
M 17.0 --- --- --- --- 21/32 0.656 ---
--- 17.50 --- --- --- 11/16 0.688 ---
M 18.0 --- 27.00 --- 27.00 11/16 0.688 ---
M 19.0 --- --- --- --- 3/4 0.750 1-1/8
M 20.0 --- 30.00 32.00 30.00 3/4 0.750 1-1/8
--- 20.64 --- --- --- 13/16 0.813 ---
M 21.0 --- --- --- --- --- 0.827 ---
M 22.0 --- 34.00 36.00 32.00 7/8 0.875 1-5/16
M 23.0 --- --- --- --- 29/32 0.906 ---
M 24.0 --- 36.00 41.00 36.00 15/16 0.938 1-1/2
M 25.0 --- 36.00 41.00 36.00 1 1.000 1-1/2
M 26.0 --- --- --- --- 1-1/16 1.0625 ---
M 27.0 --- 41.00 46.00 41.00 1-1/8 1.125 1-11/16
M 30.0 --- --- --- --- 1-3/16 1.188 ---
M 31.0 31.75 46.00 50.00 46.00 1-1/4 1.250 1-7/8
M 32.0 --- 46.00 50.00 46.00 1-1/4 1.250 1-7/8
M 33.0 34.00 50.00 --- 50.00 1-3/8 1.375 2-1/16
--- 35.00 --- --- --- 1-3/8 1.375 2-1/16
M 36.0 38.00 55.00 60.00 55.00 1-1/2 1.500 2-1/4
M 39.0 39.69 60.00 --- 60.00 1-9/16 1.562 ---
--- 40.00 --- --- --- 1-9/16 1.562 ---
--- 41.00 --- --- --- 1-5/8 1.625 ---
M 42.0 42.86 65.00 --- 65.00 1-11/16 1.688 ---
M 45.0 --- 70.00 --- 70.00 1-3/4 1.75 2-5/8
M 48.0 --- 75.00 --- 75.00 --- 1.88 ---
M 50.0 --- --- --- --- 2 2.000 ---
M 52.0 --- 80 --- 80 2 2.000 3
M 54.0 --- --- --- --- 2-1/8 2.125 ---
M 56.0 57.00 85 --- 85 2-1/4 2.250 3-3/8
M 60.0 --- 90 --- 90 2-3/8 2.375 ---
--- 63.50 95 --- 95 2-1/2 2.500 3-3/4
M 64.0 --- 95 --- 95 2-1/2 2.500 3-3/4
M 68.0 --- 100 --- 100 --- --- ---
M 72.0 --- 105 --- 105 2-3/4 --- 4-1/8
M 76.0 --- 110 --- 110 --- --- ---
M 80.0 --- 115 --- 115 3 3.000 4-1/2
M 85.0 --- 120 --- 120 --- --- ---
M 90.0 --- 130 --- 130 --- --- ---
M 95.0 --- 135 --- 135 --- --- ---
M 100.0 --- 145 --- 145 --- --- ---
M 105.0 --- 150 --- 150 --- --- ---
M 110.0 --- 155 --- 155 --- --- ---

Table values compiled from: 

Table labels: 

  • AS: Australian Standard 
  • DIN: Deutsches Institut für Normung (German Standard) 
  • SAE: Society of Automotive Engineers (American Standard originally established for the automotive industry) 
  • AF: Across Flats 
  • UNC: Unified National Coarse  
  • UNF: Unified National Fine 

Notes: 

  • Not all metric fasteners have imperial equivalents, and vice versa. 
  • Some metric values are close enough to essentially have the same imperial counterpart. In this case, you can use the same spanner size on them.