Standard metric screws and their Imperial equivalents

dm = diameter (mm)
pm = pitch (mm)
di = diameter (in)
pi = pitch (tpi)
tdm = tap drill size (mm)
tdi = tap drill size (in)

 dm  x pm   ( di x  pi )    tdm ( tdi )  easily confused with

 1.6 x 0.35  (0.063 x 72.6)  1.25 (0.049)  [0-80 = 0.060 x 80]
 1.8 x 0.35  (0.071 x 72.6)  1.45 (0.057)  [1-72 = 0.073 x 72]
 2.0 x 0.40  (0.079 x 63.5)  1.60 (0.063)  [2-64 = 0.085 x 64]
 2.2 x 0.45  (0.087 x 56.4)  1.75 (0.069)  [2-56 = 0.085 x 56]
 2.5 x 0.45  (0.098 x 56.4)  2.05 (0.081)  [3-56 = 0.099 x 56]
 3.0 x 0.50  (0.118 x 50.8)  2.50 (0.098)  [4-48 = 0.112 x 48]
 3.5 x 0.60  (0.138 x 42.3)  2.90 (0.114)  [6-40 = 0.138 x 40]
 4.0 x 0.70  (0.157 x 36.3)  3.30 (0.130)  [8-36 = 0.164 x 36]
 4.5 x 0.75  (0.177 x 33.9)  3.75 (0.148)
 5.0 x 0.80  (0.197 x 31.8)  4.20 (0.165)  [10-32 = 0.190 x 32]
 6.0 x 1.00  (0.236 x 25.4)  5.00 (0.197)  [1/4-28 = 0.25 x 28]
 7.0 x 1.00  (0.276 x 25.4)  6.00 (0.236)
 8.0 x 1.25  (0.315 x 20.3)  6.75 (0.266)
 8.0 x 1.00  (0.315 x 25.4)  7.00 (0.276)  [5/16-24 = 0.3125 x 28]
10.0 x 1.50  (0.394 x 16.9)  8.50 (0.335)
10.0 x 1.25  (0.394 x 20.3)  8.75 (0.344)
12.0 x 1.75  (0.472 x 14.5)  10.25 (0.404)
12.0 x 1.25  (0.472 x 20.3)  10.75 (0.423)
14.0 x 2.00  (0.551 x 12.7)  12.00 (0.472)
14.0 x 1.50  (0.551 x 16.9)  12.50 (0.492)
16.0 x 2.00  (0.630 x 12.7)  14.00 (0.551)
16.0 x 1.50  (0.630 x 16.9)  14.50 (0.571)
18.0 x 2.50  (0.709 x 10.2)  15.50 (0.610)
18.0 x 1.50  (0.709 x 16.9)  16.50 (0.650)
20.0 x 2.50  (0.787 x 10.2)  17.50 (0.689)
20.0 x 1.50  (0.787 x 16.9)  18.50 (0.728)
22.0 x 2.50  (0.866 x 10.2)  19.50 (0.768)
22.0 x 1.50  (0.866 x 16.9)  20.50 (0.807)
24.0 x 3.00  (0.945 x  8.5)  21.00 (0.827)
24.0 x 2.00  (0.945 x 12.7)  22.00 (0.866)
27.0 x 3.00  (1.063 x  8.5)  24.00 (0.945)
27.0 x 2.00  (1.063 x 12.7)  25.00 (0.984)