Countersunk Hole Size for 100 Degree Machine Screw (ANSI Inch)

countersunk-100-machine-ansi-inch
Unsure on what size countersunk hole to use for your ANSI Inch 100 degree machine fasteners?

Then look no further!

This short post will give you the exact dimensions you need for your countersunk screws.

Jump to Chart

A countersunk hole is used for flat head fasteners which have a flat top face and then a taper down from the top face.

They are used when the top of a screw or bolt needs to be flush with the surface of the material it is inserting.

For example, a flat head screw with a countersunk hole sits flush with or just below the surface, whereas a screw that is not countersunk will sit above the surface:
 

Countersunk-Hole-vs-Clearance-Hole

An example of a flat head screw and the corresponding countersunk hole is shown in this 3D model:

Countersunk Hole
Flat Head (Countersunk) Screw

Use the image and chart below to determine what dimensions to use, all dimensions are in inches apart from the countersink angle.

For example, an ANSI Inch 9/16″ 100 degree machine screw with a normal fit countersunk hole will require a pilot hole diameter of 5/8″, a countersunk diameter of 1 10/69″, and a countersunk angle of 100°.

Countersunk-Hole-Dimensions-Diameter

Countersunk Hole Size Chart for 100 Degree Machine Fasteners (ANSI Inch)

All dimensions are in inches apart from the countersink angle.

Fastener Size (Thread)

Pilot Hole Diameter (Close Fit)

Pilot Hole Diameter (Normal Fit)

Pilot Hole Diameter (Loose Fit)

Countersink Diameter

Countersink Angle

#0- 6/79 3/32 5/42100
#1 3/37 4/45 8/7713/89100
#2 3/32 7/69 7/6216/93100
#3 5/47 8/69 9/70 1/5 100
#4 3/25 9/7014/97 9/40100
#6 2/1310/59 5/2712/43100
#8 9/5010/5113/61 1/3 100
#1015/7321/95 5/21 5/13100
1/417/64 9/3219/6436/71100
5/1621/6411/3223/6440/63100

Fastener Size (Thread)

Pilot Hole Diameter (Close Fit)

Pilot Hole Diameter (Normal Fit)

Pilot Hole Diameter (Loose Fit)

Countersink Diameter

Countersink Angle

3/825/6413/3227/6416/21100
7/1629/6415/3231/6481/91100
1/217/32 9/1639/641 1/59100
9/1619/32 5/8 43/641 10/69100
5/821/3211/1647/641 25/92100

If you want to learn more about countersunk holes, see our post here.

Looking for a Different Standard of Countersunk Hole?

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