Tolerance As Per B 16.5

The tolerances tabulated below, apply to all ANSI Flanges, APF large Diameter flanges, and the flanged ends of Welding Necks, Certain other tolerances apply to Orifice Flanges and those are as covered by American Gas Association recommendations.

Thread, Slip-on, Lap Joint and Blind Flanges

Inside Diameter Threaded Within Limits ofboring gauge
10" and smaller + 076-0
12" and larger + 01.52-0
Outside Diameter 24" or less over 24" ± 0.0625
± 0.125
Diameter of Counterbore Same as for Inside Diameter
Diameter of contact Face 1.58mm Raised Face
150# &300#
± 0.76
6.35mm Raised Face
above 300#
Tongue & Groove or
Male & Female
± 0.50
Outside Dia. of Hub 5" and Smaller + 2.28 - 0.76
6" and larger + 4.06 - 0.76
Drilling Bolt circle ± 1.52
Bolt Hole spacing ± 0.76
Eccentricity Bolt circle & Facing (with respect to bore) 2 1/2" and smaller ± 0.76
3" and larger ± 1.52
Thickness 18" and Smaller + 3.04 - 0
20" and larger + 4.82 - 0

Except where indicated, the tolerances are those established by ANSI B 16.5 and the variations are maximum. In actual practice manufacturing and inspection procedures control dimensions so closely that variations are normally much less than those listed as permitted

Welding Neck Flanges

Inside Diameter 10" and smaller 0.76
12" to 18" 1.52
20" and larger + 3.04 - 1.52
Outside Diameter 24" or less 0.0625
over 24" 0.125
Diameter of contact Face 1.5 8mm Raised Face 150#&300# 0.76
6.35 mm Raised Face above 300# Tongue & Groove or Male & Female + 0.50
Diameter of Hub at point of Welding 5" and Smaller + 2.28 - 0.76
6" and larger + 4.06 - 0.76
Drilling Bolt circle 1.52
Bolt Hole spacing 0.76
Eccentricity Bolt circle & Facing (with respect to bore 2 1/2" and smaller 0.76
3" and larger 1.52
Length thru. Hub 4" and smaller 1.52
5" to10" + 1.52 - 3.04
12" and larger + 3.04 - 4.57
Thickness 18" and smaller + 3.04 - 0
20" and larger + 4.82 - 0