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. 

 

Metric vs Imperial equivalents 

Refer to this table when cross-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 1253 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. 
  • Is the bolt still too tight even when you’re using the right spanner size? The threads might be too rusty.