Gage Block Tolerances

Standards of Accuracy
English System: Tolerances expressed in microinches (.000001") 1 millionth of an inch

Lab. Master FED.* GRADE 0-5			Webber AA FED.* GRADE 1		Webber A1 FED.* GRADE 2		Webber A FED.* GRADE 3
Length of Block (Inches)	Tolerance (Length)	Flatness & Parallelism	Tolerance (Length)	Flatness & Parallelism	Tolerance (Length)	Flatness & Parallelism	Tolerance (Length)	Flatness & Parallelism
Through 1"	±1	1	±2	2	+4 –2	4	+8 –4	5
2"	±1	1	±4	2	+8 –4	4	+16 –8	5
3"	±1	1	±5	3	+10 –5	4	+20 –10	5
4"	±1	1	±6	3	+12 –6	4	+24 –12	5
5"			±7	3	+14 –7	4	+28 –14	5
6"			±8	3	+16 –8	4	+32 –16	5
7"			±9	3	+18 –9	4	+36 –18	5
8"			±10	3	+20 –10	4	+40 –20	5
10"			±12	4	+24 –12	5	+48 –24	6
12"			±14	4	+28 –14	5	+56 –28	6
16"			±18	4	+36 –18	5	+72 –36	6
20"			±20	4	+40 –20	5	+80 –40	6
Surface Finish Equal to Quartz Flat			Surface Finish croblox® .1-.3 Steel .3-.5		Surface Finish croblox® .3 Steel .6-.8		Surface Finish .8

Metric System: Tolerances expressed in microns (0.001 mm)

Lab. Master FED.* GRADE 0-5			Webber AA FED.* GRADE 1		Webber A1 FED.* GRADE 2		Webber A FED.* GRADE 3
Length of Block (mm)	Tolerance (Length)	Flatness & Parallelism	Tolerance (Length)	Flatness & Parallelism	Tolerance (Length)	Flatness & Parallelism	Tolerance (Length)	Flatness & Parallelism
Through 25 mm	±.03	.03	±.05	.05	±.10 –.05	.10	±.20 –.10	.12
25-50 mm	±.05	.03	±.10	.05	±.20 –.10	.10	±.40 -.20	.12
50-75 mm	±.08	.03	±.13	.07	±.25 –.12	.10	±.45-.22	.12
75-100 mm	±.10	.03	±.15	.07	±.30 –.15	.10	±.60-.30	.12
125 mm	-	-	±.18	.07	±.35 –.18	.10	±.70-.35	.12
150 mm	-	-	±.20	.07	±.40 –.20	.10	±.80-.40	.12
175 mm	-	-	±.23	.07	±.45 –.22	.10	±.90-.45	.12
200 mm	-	-	±.25	.07	±.50 –.25	.10	±1.0-.50.	.12
250 mm	-	-	±.30	.10	±.60 –.30	.12	±1.2-.60	.15
300 mm	-	-	±.35	.10	±.70 –.35	.12	±1.4-.70	.15
400 mm	-	-	±.45	.10	±.90 –.45	.12	±1.8-.90	.15
500 mm	-	-	±.50	.10	±1.0 –.50	.12	±2.0-1.0	.15
Surface Finish Equal to Quartz Flat			Surface Finish croblox® .003-.008 Steel .008-.012		Surface Finish croblox® .008 Steel .015-.020		Surface Finish .020

*Starrett-Webber Standards of Accuracy are guaranteed to meet those of U.S. Federal Specifications GGG-G-15C, British Standard 4311 (1968) and 888 (1950); German Standard DIN 861 (1959)

MATERIAL COEFFICIENTS OF THERMAL EXPANSION ARE:

Chromium Carbide 4.7 x 10ˆ-6 inch/°F per inch
8.5 x 10ˆ-6 mm/°C per mm

SAE 52100 Steel 6.4 x 10ˆ-6 inch/°F per inch
11.5 x 10ˆ-6 mm/°C per mm

Ceramic 5.55 x 0ˆ-6 inch/°F per inch
10 x 10ˆ-6 mm/°C per mm

•Grades 0.5 and 1 surpass British Reference Guide

•Grades 0.5, 1, and 2 surpass German Grade 0

Reference Temperature – 68° F (20° C)
One Inch = 25.4 millimeters

Above information provided by The L.S. Starrett Co.® and The LS Starrett Co.® Webber Gage Division

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