Quick Reference Guide

Quick Reference Guide Geometric Dimensioning and Tolerancing

Zero Does Not Mean Perfect

A or A Datum Feature M Maximum Material Condition L Least Material Condition S Regardless of Feature Size P Projected Tol. Zone T Tangent Plane F Free State ST Statistical Tolerance R Radius CR Controlled Radius SR Spherical Radius S Spherical Diameter Diameter Counterbore or Spotface Countersink Dimension Origin 8X Number of places (50) Reference Dimension 50 Basic Dimension 50 Arc Length B Between A X "BY"(2 X 4 ) Depth Conical Taper Slope All Around

A1

Square Shape Datum Target

Concentricity Straightness Cylindricity Surface Profile Angularity Perpendicularity Circular Runout

Position Flatness Circularity Line Profile Symmetry Parallelism Total Runout

Based on ASME Y14.5M-1994 .265 .250 .000 M A B C Inch drawing

.000 is a starting point when the hole size is at MMC(.250). As the hole size increases, the tol. zone also increases.

2X

.255 - .260 .020 M A B C .005 M A

.020 zone

Hole Size

Tolerance Size

.250 .251 .252 .265

.000 .001 .002 .015

The upper tol. zone locates the pattern loosely from the datums. The lower tol. zone locates the holes tightly to each other and tightly to the datum(s) for orientation only; in this case perpendicularity.

center of hole must fall within both tol. zones.

.005 zone

4X

.250 -.265 Shown below on the left the datum is .990 (MMC). When the datum is .000 M A B M at MMC it gets no bonus tolerance, and so the pattern of holes as group must be on the absolute center of the datum. B Below on the right, the datum is .998, .008 1.000 larger than MMC. This gives the datum a .990 .008 bonus tolerance, which permits the pattern of holes as a group to be off center of the datum by .004.

.008 tol.

.000 tol.

.990 DATUM

.998 DATUM

NOTE: The 008 tol. zone cannot be added to the positional tol.