Countersink Gage vs. Chamfer Gage “What’s the difference?”

Countersink Gage vs. Chamfer Gage “What’s the difference?”

When should a person choose a countersink gage over a chamfer gage? Ultimately they do a similar job - both types of gages utilize a plunger and special ratio indicator to measure the top diameter of a tapered/countersink bore.

But…there is more to the story.  This article will explain the basic advantages and disadvantages of both types.

Chamfer Gage

A Chamfer Gage has a 3 blade plunger that accommodates a large range of chamfer angles: from 0-90° or 90-127° (depending on the model) and diameters in up to 1” rangesSee table  

within ± .001" in 0°-90° models
within ± .002" in 90°-127° models

Analog Indicator: .001" graduation

(+) Relatively long range and versatile.

(-) Long range means the dial indicator will have a rev counter. You will need to count the 'revs" on a dial chamfer gage to get your reading.

(+) You can “set” a chamfer gage on any precision, flat surface: surface plate, gage block or face of a ring gageIf desired, a special sharp-edge ring gage can be made to the target I.D.

(-) Since the chamfer gage covers a wide range of diameters and does not have a precision conical plunger, you will not have as sure of a “fit” into the bore as you would with a countersink gage.

(+) The three blade design of the chamfer gage results in a slotted base to allow for part measurement below the maximum range of the chamfer gage.

Countersink Gage

A Countersink Gage is most popular in the aerospace industry and has a solid cone (under normal circumstances) ground to an exact angle that measures a specific range of countersink diameters in approximately .200” steps.  See table

± .0005" or ± .015mm

Analog Indicator: .002" graduation

(+) The countersink gage is designed to measure the very top I.D. of a bore but also verifies the angle of the countersink with its precision ground cone.  If there is some problem with the actual countersink angle itself, you will get a bad reading for the I.D. since the two are related.   Unlike the chamfer gage, you are getting two measurements for the price of one: form and diameter.

(-) Since the measuring range of the dial indicator is relatively small on an analog countersink gage, you cannot "set" the gage on a flat surface - A sharp-edge setting ring gage must be used and they are included with the analog models.
Note: This is not required for a digital countersink gage which has a larger range indicator.

(+) Analog/Dial countersink gages utilize a 1 rev, direct read indicator, so there no need to count revolutions.

(-) Since a countersink gage has a smaller measuring range than a chamfer gage, you will need to purchase multiple countersink gages if you have a wide range of countersink diameters to measure.

(-) The full form, conical design of the gage plunger results in a base with hole instead of a slotted base like the chamfer gage.  This does not allow for part measurement with an O.D. below the maximum range of the countersink gage because the part would be swallowed by the hole in the base of the countersink gage.


Question: Could you use a chamfer gage to measure the top diameter of a countersink bore?  The answer is yes.  However, as stated, the countersink gage checks countersink angle and diameter at the same time. The chamfer gage will not check the angle because it’s plunger only contacts at the very top of the bore.

Note: The plunger tip of the chamfer gage and countersink gage are not sharp.  To compensate for the truncated plunger, a 'set to" number is located on the back of the chamfer gage which represents how much of the plunger was purposely removed.  Dial countersink gages come with a setting ring so a "set to" number is not needed.  However, a digital countersink gage, which can be mastered on a precision flat surface like the chamfer gage, will have a "set to" number.

If you any questions on this subject contact us, or leave a comment below!