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Standard

FEPA-D / ISO 6106

Diamond grain grading

FEPA-D (ISO 6106) grades diamond grain by a particle-size band, not a single number. Each grade is an upper-to-lower micron range from the sieve standard, recovered from the Engis reprint of ISO 6106 Table 2 and cross-checked. The standard stops giving a uniform designation below D46.

Each grade below shows its size in microns, its spread (the published distribution, where a maker or standard gives one; most makers publish none), and where that size lands on the reference scale, a shared yardstick for reading grit numbers across makers.

Particle sizemicrons, log
10050
coarserfiner
inkmeasured or standardmaker figureour estimate
shapeknown distributionpoint, spread unknown
D851 (20/25 mesh)Standard-defined
median
780 µm

spread 710 to 850 µm · reference scale about #20

D711 (25/30 mesh)Standard-defined
median
655 µm

spread 600 to 710 µm · reference scale about #30

D601 (30/35 mesh)Standard-defined
median
550 µm

spread 500 to 600 µm · reference scale about #30

D501 (35/40 mesh)Standard-defined
median
462.5 µm

spread 425 to 500 µm · reference scale about #40

D426 (40/45 mesh)Standard-defined
median
390 µm

spread 355 to 425 µm · reference scale about #40

D356 (45/50 mesh)Standard-defined
median
327.5 µm

spread 300 to 355 µm · reference scale about #50

D301 (50/60 mesh)Standard-defined
median
275 µm

spread 250 to 300 µm · reference scale about #60

D251 (60/70 mesh)Standard-defined
median
231 µm

spread 212 to 250 µm · reference scale about #70

D213 (70/80 mesh)Standard-defined
median
196 µm

spread 180 to 212 µm · reference scale about #80

D181 (80/100 mesh)Standard-defined
median
165 µm

spread 150 to 180 µm · reference scale about #90

D151 (100/120 mesh)Standard-defined
median
137.5 µm

spread 125 to 150 µm · reference scale about #110

D126 (120/140 mesh)Standard-defined
median
115.5 µm

spread 106 to 125 µm · reference scale about #130

D107 (140/170 mesh)Standard-defined
median
98 µm

spread 90 to 106 µm · reference scale about #150

D91 (170/200 mesh)Standard-defined
median
82.5 µm

spread 75 to 90 µm · reference scale about #170

D76 (200/230 mesh)Standard-defined
median
69 µm

spread 63 to 75 µm · reference scale about #200

D64 (230/270 mesh)Standard-defined
median
58 µm

spread 53 to 63 µm · reference scale about #240

D54 (270/325 mesh)Standard-defined
median
49 µm

spread 45 to 53 µm · reference scale about #270

D46 (325/400 mesh)Standard-defined
median
41.5 µm

spread 38 to 45 µm · reference scale about #310