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Screws · ASME B18.6.3 · Application guide

What Are Flat Head Machine Screws, UNC (Slotted and Phillips) Used For?

Typical applications, the industries that specify flat head machine screws, unc (slotted and phillips), and how to choose the right size, material and finish for the joint.

Flat Head Machine Screws, UNC (Slotted and Phillips) are used for inch flat countersunk head machine screws with UNC thread, slotted or Phillips. They are manufactured to ASME B18.6.3, and the choice of size, property class and finish is driven by the load in the joint and the environment it sits in.

Primary duty
Inch flat countersunk head machine screws with UNC thread, slotted or Phillips
Governing standard
ASME B18.6.3
Screw size range
1/2" to #12
Category
Screws

Application notes are general engineering guidance. Verify the property class and any approval requirement against your own design calculation.

What Are Flat Head Machine Screws, UNC (Slotted and Phillips) Used For? application image

Flat Head Machine Screws, UNC (Slotted and Phillips) are used primarily for inch flat countersunk head machine screws with UNC thread, slotted or Phillips. This page lists the industries and assemblies where they are specified, the selection criteria that matter for each application, installation practice, and the cases where a different fastener type is the correct choice. Parts are supplied to ASME B18.6.3. Stocked across roughly 1 to 12, they cover general to heavy-duty work.

Typical Applications for Flat Head Machine Screws, UNC (Slotted and Phillips)

The most common settings where these are specified:

  • Electronics: panels.
  • Appliances: inch hardware.
  • Hardware: hinges.
  • Aerospace ground support: flush panels.

How to Specify Flat Head Machine Screws, UNC (Slotted and Phillips) for Your Application

  • Size: Match the nominal size to the mating thread or hole. This product spans 1–12; check the full table below for the exact dimensions of each size.
  • Drive & head: Pick the drive (socket, cross, slot) and head style for the tool access and seating surface; a recessed drive resists cam-out under power tools.
  • Environment: For damp, coastal or chemical exposure prefer A4/316 stainless or a suitable coating; indoors, plated steel or A2 is usually sufficient.
  • Standard: This product is supplied to ASME B18.6.3. Quoting the standard on your order guarantees interchangeable dimensions between suppliers.

Installation & Assembly Practice

  • Match the driver exactly to the recess (PH ≠ PZ; hex key sizes per ISO 2936) and keep the tool axial — side load is the main cause of stripped drives.
  • In tapped holes, engage a thread length of at least 1× the nominal diameter in steel, 2× in aluminum.
  • Set power tools to a torque that seats the head without embedding it into the mating surface.

Common Selection Mistakes with Flat Head Machine Screws, UNC (Slotted and Phillips)

  • Under-sizing the drive for the installation torque — a small recess at high torque strips before the screw is seated.
  • Using a countersunk head in thin sheet where the countersink removes most of the load-bearing material.
  • Specifying stainless in high-strength duty: A2-70 is roughly class 7 steel, not a 10.9 substitute.

Where Flat Head Machine Screws, UNC (Slotted and Phillips) Are Not the Right Choice

Not for high-preload structural joints (use a property-class bolt and nut), and not in thin sheet where a self-drilling or self-tapping type suits better.

Custom manufacturing · Made to drawing

Need a flat head machine screws, UNC (slotted and phillips) outside the standard range?

Lengths and thread lengths outside the standard table are the commonest request, followed by a drive the standard does not offer and a head marked with your own part number. Made by cold heading or warm forging.

Minimum order from 2,000 pieces; samples within 7 days of drawing approval.

Custom screw manufacturingSend a drawing

Technical Drawing

Customize the parameters below — every spec field is editable, and the drawing redraws to match the values you choose. Changing the size will snap the other fields to that size's standard values; you can then override any individual value.

Dimensioned line drawing of #0 Flat Head Machine Screws, UNC (Slotted and Phillips) to ASME B18.6.3. Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected.
Type
Slotted countersunk flat head screws
Pitch P (mm)
0.318
b (mm)
3.696
Head diameter dk (mm)
2.845
dk_mean (mm)
2.642
Head height k (mm)
0.889
n_min (mm)
0.495
r (mm)
0.152
t_mean (mm)
0.318
Length range l (in)
1/16"~1 1/2"
Sends the selected values to the quote form below.

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The form below follows the current technical drawing configuration. Change the drawing values above and the request details update automatically.

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Specification
Business Information

Dimensions & Specifications (ASME B18.6.3)

SizeTypePitch P (mm)b (mm)Head diameter dk (mm)dk_mean (mm)Head height k (mm)n_min (mm)r (mm)t_mean (mm)Length range l (in)Reference standard
#0Slotted countersunk flat head screws0.3183.6962.8452.6420.8890.4950.1520.3181/16"~1 1/2"ASME B18.6.3
#0Cross recessed countersunk flat head screws0.3183.6962.8452.6420.8890.4950.1520.3181/16"~1 1/2"ASME B18.6.3
#1Slotted countersunk flat head screws0.3974.4973.483.2641.0920.5720.1850.3941/16"~1 1/2"ASME B18.6.3
#1Cross recessed countersunk flat head screws0.3974.4973.483.2641.0920.5720.1850.3941/16"~1 1/2"ASME B18.6.3
#2Slotted countersunk flat head screws0.4545.2984.1153.8861.2950.6860.2180.4831/16"~2 1/2"ASME B18.6.3
#2Cross recessed countersunk flat head screws0.4545.2984.1153.8861.2950.6860.2180.4831/16"~2 1/2"ASME B18.6.3
#3Slotted countersunk flat head screws0.5296.0984.754.4961.4990.7870.2510.5591/8"~2 1/2"ASME B18.6.3
#3Cross recessed countersunk flat head screws0.5296.0984.754.4961.4990.7870.2510.5591/8"~2 1/2"ASME B18.6.3
#4Slotted countersunk flat head screws0.6356.8995.3855.1181.7020.8890.2840.6351/8"~4"ASME B18.6.3
#4Cross recessed countersunk flat head screws0.6356.8995.3855.1181.7020.8890.2840.6351/8"~4"ASME B18.6.3
#5Slotted countersunk flat head screws0.6357.76.025.741.9050.9910.3180.7113/16"~4"ASME B18.6.3
#5Cross recessed countersunk flat head screws0.6357.76.025.741.9050.9910.3180.7113/16"~4"ASME B18.6.3
#6Slotted countersunk flat head screws0.7948.5016.6556.352.1081.1050.3510.7871/8"~4"ASME B18.6.3
#6Cross recessed countersunk flat head screws0.7948.5016.6556.352.1081.1050.3510.7871/8"~4"ASME B18.6.3
#8Slotted countersunk flat head screws0.79410.1027.9257.5822.541.2570.4170.941/8"~5"ASME B18.6.3
#8Cross recessed countersunk flat head screws0.79410.1027.9257.5822.541.2570.4170.941/8"~5"ASME B18.6.3
#10Slotted countersunk flat head screws1.05811.7049.1958.8262.9461.3970.4831.1053/16"~8"ASME B18.6.3
#10Cross recessed countersunk flat head screws1.05811.7049.1958.8262.9461.3970.4831.1053/16"~8"ASME B18.6.3
#12Slotted countersunk flat head screws1.05813.30610.46510.0583.3531.5620.5491.2571/4"~8"ASME B18.6.3
#12Cross recessed countersunk flat head screws1.05813.30610.46510.0583.3531.5620.5491.2571/4"~8"ASME B18.6.3
1/4"Slotted countersunk flat head screws1.2715.412.11611.6713.8861.7650.6351.4733/8"~10"ASME B18.6.3
1/4"Cross recessed countersunk flat head screws1.2715.412.11611.6713.8861.7650.6351.4733/8"~10"ASME B18.6.3
5/16"Slotted countersunk flat head screws1.41119.2515.16414.6434.8511.9810.7941.8541/2"~10"ASME B18.6.3
5/16"Cross recessed countersunk flat head screws1.41119.2515.16414.6434.8511.9810.7941.8541/2"~10"ASME B18.6.3
3/8"Slotted countersunk flat head screws1.58723.118.21217.6155.8422.2230.9532.2351/2"~12"ASME B18.6.3
3/8"Cross recessed countersunk flat head screws1.58723.118.21217.6155.8422.2230.9532.2351/2"~12"ASME B18.6.3
7/16"Slotted countersunk flat head screws1.81426.9519.30418.7335.6642.2231.1112.1463/4"~12"ASME B18.6.3
7/16"Cross recessed countersunk flat head screws1.81426.9519.30418.7335.6642.2231.1112.1463/4"~12"ASME B18.6.3
1/2"Slotted countersunk flat head screws1.95430.820.70120.0665.6642.5021.272.1343/4"~12"ASME B18.6.3
1/2"Cross recessed countersunk flat head screws1.95430.820.70120.0665.6642.5021.272.1343/4"~12"ASME B18.6.3
9/16"Slotted countersunk flat head screws2.16734.6523.67322.9876.6042.7941.4292.5023/4"~12"ASME B18.6.3
9/16"Cross recessed countersunk flat head screws2.16734.6523.67322.9876.6042.7941.4292.5023/4"~12"ASME B18.6.3
5/8"Slotted countersunk flat head screws2.30938.526.6725.9087.5693.1621.5872.8573/4"~14"ASME B18.6.3
5/8"Cross recessed countersunk flat head screws2.30938.526.6725.9087.5693.1621.5872.8573/4"~14"ASME B18.6.3
3/4"Slotted countersunk flat head screws2.5446.232.63931.759.4493.5561.9053.5811"~14"ASME B18.6.3
3/4"Cross recessed countersunk flat head screws2.5446.232.63931.759.4493.5561.9053.5811"~14"ASME B18.6.3

Video: What Are Flat Head Machine Screws, UNC (Slotted and Phillips) Used For? in use

Third-party video, selected automatically for this topic. It is not produced by Engineering Hardware and is not a specification source — use the tables on this page for dimensional data.

Inside the plant

Manufactured in our own plant

This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided.

  1. Wire rod feeding into a cold heading machine
    01

    Cold heading

    Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail.

    Head dimensions and under-head radius checked at set-up and per shift.

  2. Thread rolling machine producing bolt threads
    02

    Thread rolling

    Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch.

    Go / no-go ring gauges to ISO 965 tolerance class 6g.

  3. Baskets of bolts staged for heat treatment
    03

    Heat treatment

    Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it.

    Core hardness and tensile tested per lot to ISO 898-1.

  4. Zinc plated bolts in a treatment basket
    04

    Surface treatment

    Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list.

    Coating thickness and neutral salt spray hours to ISO 9227.

Frequently Asked Questions

What material should Flat Head Machine Screws, UNC (Slotted and Phillips) be for outdoor use?

For damp, coastal or chemical environments specify A4 (316) stainless or a suitably coated steel. For indoor or dry use, A2 (304) stainless or zinc-plated steel is normally adequate.

Are Flat Head Machine Screws, UNC (Slotted and Phillips) made to a recognized standard?

Yes — they are manufactured to ASME B18.6.3, so dimensions are interchangeable between suppliers when you quote the standard on your order.

What are Flat Head Machine Screws, UNC (Slotted and Phillips) used for?

Inch flat countersunk head machine screws with UNC thread, slotted or Phillips. They are supplied to ASME B18.6.3.

Which industries use Flat Head Machine Screws, UNC (Slotted and Phillips)?

They are commonly specified in electronics, appliances and hardware, among other sectors.

Can I get a quote for Flat Head Machine Screws, UNC (Slotted and Phillips) in the size and material I need?

Yes. Use the technical drawing and quote form on this page to set the size and options, then send the exact configuration to our team for pricing and lead time.