Countersinking & Counterboring Services

Improve part fit and finish with these practical guides to countersinking and counterboring at PCBWay. Based on our experience producing millions of parts, these best practices and tips will help you select suitable features and achieve reliable results during production.

10+ Materials

0.1mm-10mm Thickness

3-5 Days

Lead Time

Rapid Prototyping Sheet Metal Countersink & Counterbore

Countersink & Counterbore sizing and options

Part Sizes

Countersink and counterbore operations machine tapered or recessed cavities to allow fastener heads to sit flush below the part surface. Common included angles include 45° and 90°, with machined features held within defined dimensional tolerances.

Large diameter:

20 mm
Small diameter:

3.5 mm
Countersink angles:

45°, 90°
Tolerance:

±0.3 mm

10+ Materials(0.1mm-10mm)

Compatible services

Multiple Hole Machining Options · Matched to Your Needs

Conical · Flush

Countersink: A conical recess is machined around the hole to accommodate flat-head screws, allowing the fastener head to sit flush with or below the surface.

Designed for flat-head screw installation.
Enables flush-mount fastener applications.
Delivers smooth, unobstructed outer surfaces.
Conical chamfer profile matches flat-head screw geometry.

Conical · Flush

Countersink: A conical recess is machined around the hole to accommodate flat-head screws, allowing the fastener head to sit flush with or below the surface.

Cylindrical · Recessed

Counterbore: A cylindrical recess with a flat bottom is machined around the hole to accommodate socket-head cap screws and other cylindrical-head fasteners.

Available Materials For Countersink

In addition to the materials listed below, we also accept customer-supplied materials for processing.

Aluminum

It is strong, which makes it ideal for mechanical parts, and its oxidized outer layer is resistant to corrosion from the elements.

Stainless steel

Excellent wear and corrosion resistance.

Mild steel

Since its carbon and alloying element content are relatively low, there are several properties it has that differentiate it from higher carbon and alloy steels.

Copper

Strength, conductivity, corrosion resistance, machinability, and ductility make copper one of the most versatile materials for a broad range of applications.

Titanium

Advantages: lightweight, non-magnetic, resistant to salt spray and chloride ion corrosion, self-repairing surface passive film, and capable of TIG welding.

PMMA (Acrylic)

The highest quality PMMA sheets are produced by cell casting, but in this case, the polymerization and molding steps occur concurrently.

Sheet metal

Aluminum 5052-H32: Aluminum 5052-H32 is an aluminium alloy, primarily alloyed with magnesium and chromium.

Silver white

Sheet metal

Aluminum 6061-T6: Aluminum 6061-T6 is an alloy that is suitable for hot forging. The billet is heated through an induction furnace and forged using a closed die process.

Silver white

Sheet metal

Stainless steel 304: Stainless Type 304 is one of the most versatile and commonly used grades of stainless steel.

Silver

Sheet metal

Stainless Steel 316/316L: Stainless Type 316 is a standard molybdenum-bearing austenitic stainless steel grade.

Silver

Sheet metal

Stainless steel 201: Stainless steel 201, with certain acid and alkali resistance, high density, no bubbles, no pinholes, etc.

Silver

Sheet metal

Stainless Steel 301: Type 301 is an austenitic stainless steel with a nominal composition of 17 percent chromium and 7 percent nickel, which provides good strength and ductility when cold worked.

Silver

Sheet metal

Mild steel 1018: Mild steel 1018 is a widely used alloy with good machinability, weldability, toughness, strength, but it’s susceptible to corrosion on the surface.

Silver gray

Sheet metal

Copper C110: Copper C110, being a tough pitch copper alloy, is not easily welded or brazed because it suffers from embrittlelment when heated in a reducing atmosphere.

Copper

Sheet metal

Copper 260 (Brass): C260 brass is the most ductile of the brasses and is used in greater quantity than any other copper-zinc alloy.

Brass

Sheet metal

Copper 101: Copper alloy C101 is also known as HC or high conductivity copper.

Copper

Sheet metal

Titanium Gr1(TA1): Titanium Gr1(TA1) is an industrial-grade pure titanium sheet with good ductility, making it suitable for sheet metal bending and forming. It is resistant to chloride ion corrosion, and welding requires inert gas protection.

Silver

Sheet metal

Titanium Gr5 (TC4): Titanium Gr5 (TC4) titanium sheet offers high strength and fatigue resistance, making it suitable for load-bearing sheet metal structural components; however, it has poor ductility, making it difficult to bend and form, and requires argon gas shielding during welding.

Silver

Sheet metal

PMMA (Acrylic): Polymethyl methacrylate(PMMA), is a kind of high molecular polymer, also known as acrylic or plexiglass.

Transparent

Our Surface Finishes For Welding Parts

With our precision welding capabilities, sheet metal assemblies gain strong, reliable joints and a clean finished appearance,

Standard (As-Milled) (Ra 125μin): The finish option with the quickest turnaround. Sharp edges and burrs would be removed by default. (If you need parts with sharp edges and burrs, please remark below or note on 2D drawing). Surface finish is comparable to 125 uin Ra finish.

Copper C110
Stainless steel 304
Aluminum 5052-H32
Copper 260 (Brass)

More Surface Finishes

Countersink Capability

Process	Description
Large diameter	20 mm
Small diameter	3.5 mm
Countersink angles	45°, 90°
Tolerance	±0.3 mm

We offer competitive pricing, with bulk purchase discounts of up to 80%.

Aluminum 5052

50*50mm: Laser cutting

Qty 1:

$12.45/pc
Qty 100:

$2.49/pc

Stainless Steel 304

100*100mm: Laser cutting, Bending

Qty 1:

$20/pc
Qty 100:

$4/pc

Mild Steel 1018

200*200mm: Laser cutting, Bending, Threads, Inserts

Qty 1:

$50/pc
Qty 100:

$10/pc

Copper C110

200*200mm: Laser cutting, Bending, Threads, Inserts

Qty 1:

$70/pc
Qty 100:

$14/pc

Countersink & Counterbore Holes Design Guidelines

This design guide provides structural engineers and mechanical designers with essential Design for Manufacturability (DFM) rules for Countersink (CSINK) and Counterbore (CBORE) holes in sheet metal fabrication and CNC machining. Following these geometric standards helps prevent knife-edge cutting, material tearing, bolt head protrusion, and engineering question (EQ) delays—ensuring a 100% first-pass review rate and fast delivery schedules.

1. Countersink (CSINK) vs. Counterbore (CBORE) Explained

When designing parts for flush or recessed fasteners, choosing the correct hole geometry is critical to achieving functional performance and clean aesthetics.

Countersink Hole (CSINK): A conical basin cut into the surface to accept flat-head or undercut countersunk screws. The primary goal is to seat the screw head completely flush with or slightly below the outer surface of the part.
Counterbore Hole (CBORE): A flat-bottomed, cylindrical enlargement of a hole designed to accommodate cylindrical screw heads, such as Socket Head Cap Screws (SHCS), allowing the fastener to sink entirely below the material surface.

Countersink (CSINK) vs Counterbore (CBORE) Explained, hole geometry for recessed fasteners

2. Countersink Angle Standards: Metric vs. Imperial

A common cause of assembly interference is pairing screws with the wrong countersink angle. Always align your CAD design with the corresponding thread standard:

90° Angle (Metric Standard): The universal standard for all Metric countersunk screws (e.g., M2.5, M3, M4, M5, M6 per DIN 965 / ISO 7046).
82° Angle (Imperial/US Standard): The standard angle for Unified National Thread fasteners in North America (e.g., #4-40, #6-32, #8-32, 1/4"-20 UNC).
100° Angle (Aero & Thin Sheet Special): Used primarily in aerospace applications and ultra-thin sheet metal where shallow fastener heads are required to prevent punch-through.

3. Sheet Metal Countersinking: Critical DFM Rules

Processing countersinks on laser-cut sheet metal requires strict adherence to sheet thickness limits and feature clearances.

Rule 1: The "Knife-Edge" & Minimum Material Margin

Never allow a countersink to cut entirely through a piece of sheet metal. Leaving zero cylindrical wall thickness creates a razor-thin knife-edge at the bottom of the hole, leading to burrs, tool chatter, hole enlargement, and structural tearing during assembly.

Minimum Web Thickness: Always preserve a straight cylindrical wall height of at least 0.50 mm (0.020") at the bottom of the countersink.
Maximum Countersink Depth: The countersink head depth (H_cs) should not exceed 60% to 70% of the total sheet thickness (T).

Max Depth (H_cs) ≤ 0.70 × T

(Note: If sheet thickness is less than the countersink depth, evaluate using Press/Dimpled Countersinks or PEM Clinch Studs instead.)

Rule 2: Edge Distance & Bend Clearance

Tensile forces during bending can deform nearby countersunk holes, preventing flat-head screws from sitting flush.

Distance to Bend Line: The edge of the countersink rim must be placed at a distance ≥ (1/2 × Bend Die Opening + 2 × T) away from any fold lines.

4. CNC Machined Countersink & Counterbore Depth Rules

For solid CNC-milled parts, tool access and clearance tolerances dictate design quality.

CBORE Diameter Clearance: Always size the counterbore diameter (D_cbore) 0.5 mm to 1.0 mm (0.020" to 0.040") larger than the actual screw head diameter to allow for socket driver clearance and anodizing/plating thickness.
CBORE Depth Margin: Model the counterbore depth 0.2 mm to 0.4 mm deeper than the screw head height. This ensures the screw sits slightly below the surface, even with manufacturing tolerances on the fastener itself.

5. Recommended Countersink & Counterbore Size Chart

Use the following standard dimensions when modeling 3D CAD geometries for Metric and Imperial fasteners:

Metric Standards (90° Countersink / Standard Counterbore)

Fastener Size	Clearance Hole (mm)	CSINK Major Dia (mm)	CSINK Angle	CBORE Dia (mm)	CBORE Depth (mm)
M2.5	2.70 mm	5.50 mm	90°	5.00 mm	2.70 mm
M3	3.30 mm	6.50 mm	90°	6.00 mm	3.30 mm
M4	4.50 mm	8.60 mm	90°	7.50 mm	4.40 mm
M5	5.50 mm	10.80 mm	90°	9.50 mm	5.40 mm
M6	6.60 mm	12.80 mm	90°	11.00 mm	6.50 mm

Imperial Standards (82° Countersink / Standard Counterbore)

Fastener Size	Clearance Hole (inch)	CSINK Major Dia (inch)	CSINK Angle	CBORE Dia (inch)	CBORE Depth (inch)
#4-40 UNC	0.128"	0.225"	82°	0.218"	0.112"
#6-32 UNC	0.149"	0.279"	82°	0.250"	0.138"
#8-32 UNC	0.177"	0.332"	82°	0.298"	0.164"
1/4"-20 UNC	0.266"	0.507"	82°	0.438"	0.250"