18-8 Stainless Steel Flat Head Socket Cap Screws with Nylon Insert

18-8 stainless steel flat head socket cap screws with nylon insert combine a countersunk flat head design with a factory-installed nylon locking element that provides prevailing torque during installation. The flat head seats flush within a properly prepared countersunk hole for a smooth finished surface, while the internal hex drive allows installation where external wrench clearance is limited. The nylon insert helps increase resistance to thread loosening caused by vibration, repeated movement, and dynamic loading.

Manufactured from 18-8 stainless steel, these fasteners provide general corrosion resistance for many industrial environments exposed to moisture, humidity, or routine washdown. They are commonly specified for machinery, automation equipment, robotics, industrial enclosures, instrumentation, fixtures, conveyor systems, transportation equipment, maintenance repairs, and OEM assemblies where both corrosion resistance and flush-mounted installation are important.

Flat head socket cap screws are designed for use in countersunk holes, allowing the installed fastener to sit flush with the surrounding surface. Proper fastener selection should consider thread size, screw length, countersink dimensions, head diameter, head height, hex socket size, mating-thread engagement, installation access, and service conditions. The nylon insert provides prevailing torque but should not be considered a substitute for proper joint design or installation practices.

Cold Headers supplies 18-8 stainless steel flat head socket cap screws with nylon insert in a broad range of inch thread sizes and lengths, including uncommon and difficult-to-source configurations. Individual product pages provide verified thread size, screw length, nominal body diameter, head diameter, head height, hex socket size, and additional engineering information where available.

Why Choose Flat Head Socket Cap Screws with Nylon Insert?

  • Factory-installed nylon insert: Provides prevailing torque to help resist thread loosening.
  • Countersunk flat head: Installs flush within a properly prepared countersunk hole.
  • 18-8 stainless steel: Offers general corrosion resistance for many industrial environments.
  • Internal hex drive: Allows installation where external wrench clearance is limited.
  • Verified engineering dimensions: Product pages provide thread size, length, head dimensions, and hex socket size where available.

Selecting the Correct Flat Head Socket Cap Screw

Begin by confirming the required thread size and screw length. Review the countersink dimensions, head diameter, head height, hex socket size, installation clearance, mating-thread engagement, and operating environment before selecting a fastener. Final selection should reflect the mechanical and environmental requirements of the completed assembly.

Cold Headers Inc. has supplied specialty industrial socket fasteners since 1962. Our catalog helps engineers, distributors, maintenance teams, and purchasing professionals locate exact sizes, uncommon lengths, and difficult-to-find flat head socket cap screws with nylon insert without unsupported inventory claims.

Call 773-775-7900 or email Sales@coldheaders.com for pricing, availability, or a quote.

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4-40 x 1/4 18-8 Stainless Steel Flat Head Cap Screw with Nylon Insert
List Price (per 100 pieces) $92.50
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4-40 x 3/8 18-8 Stainless Steel Flat Head Cap Screw with Nylon Insert
List Price (per 100 pieces) $93.00
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4-40 x 1/2 18-8 Stainless Steel Flat Head Cap Screw with Nylon Insert
List Price (per 100 pieces) $93.50
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4-40 x 5/8 18-8 Stainless Steel Flat Head Cap Screw with Nylon Insert
List Price (per 100 pieces) Call or Email for Pricing
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4-40 x 3/4 18-8 Stainless Steel Flat Head Cap Screw with Nylon Insert
List Price (per 100 pieces) Call or Email for Pricing
Description N/A

4-40 x 1/4 18-8 Stainless Steel Flat Head Cap Screw with Nylon Insert uses an 82-degree countersunk head for fastening where surface projection must be minimized. The 82-degree flat head needs a matching countersink cut cleanly and concentrically so the cone bears correctly and the head seats true.

Typical applications include sliding machine covers, flush access panels, and service plates, where nothing proud should catch passing material or hands. When chloride-heavy or saltwater-adjacent service drives material selection, ask Cold Headers about non-catalog 316 stainless nylon-insert options.

The 18% chromium and 8% nickel austenitic stainless material is commonly selected for general corrosion resistance, clean appearance, and ordinary washdown exposure. Cold Headers has supported specialty socket fastener sourcing since 1962, including exact stainless sizes and uncommon lengths.

Technical Highlights

  • Material: 18-8 Stainless Steel
  • Thread Size: 4-40
  • Length (overall - includes head): 1/4 in.
  • Head Style: 82° Countersunk Flat
  • Drive Type: Internal Hex
  • Locking Feature: Nylon insert providing prevailing torque
  • Nylon Insert Diameter (P): 1/16 in.
  • Nylon Insert Location (N): 7/64 in. +/-1/2 pitch
  • Head Dimensions: ASME B18.3

Call 773-775-7900 or email Sales@coldheaders.com for pricing, availability, or a quote.

 		N/A

4-40 x 3/8 18-8 Stainless Steel Flat Head Cap Screw with Nylon Insert is measured overall, so the listed length includes the flat head. Flat head screw lengths are measured overall, head included, so this listed length is the total installed screw length. The 82-degree flat head needs a matching countersink cut cleanly and concentrically so the cone bears correctly and the head seats true.

In food equipment surfaces, wipe-down panels, or stainless guards, the internal hex drive supports top-side installation after the countersink is prepared. For a low-profile head without cutting a countersink, compare 18-8 Button Head Socket Cap Screws with Nylon Insert.

The 18% chromium and 8% nickel austenitic stainless material is commonly selected for general corrosion resistance, clean appearance, and ordinary washdown exposure. For supported flat head cap-screw requests, nylon inserts are installed in-house at the Chicago facility.

Technical Highlights

  • Material: 18-8 Stainless Steel
  • Thread Size: 4-40
  • Length (overall - includes head): 3/8 in.
  • Head Style: 82° Countersunk Flat
  • Drive Type: Internal Hex
  • Locking Feature: Nylon insert providing prevailing torque
  • Nylon Insert Diameter (P): 1/16 in.
  • Nylon Insert Location (N): 7/64 in. +/-1/2 pitch
  • Head Dimensions: ASME B18.3

Call 773-775-7900 or email Sales@coldheaders.com for pricing, availability, or a quote.

 		N/A

4-40 x 1/2 18-8 Stainless Steel Flat Head Cap Screw with Nylon Insert combines stainless material, internal hex drive access, and a nylon locking pellet. A countersunk head bears on the cone rather than a broad underside, so clamp load should not be treated like a full socket head cap screw. Flat head screw lengths are measured overall, head included, so this listed length is the total installed screw length.

This size is often reviewed for packaging machinery guards, changeover plates, and transfer covers when stainless material, a flush head, and locking friction are all specified. For a low-profile head without cutting a countersink, compare 18-8 Button Head Socket Cap Screws with Nylon Insert.

The 18% chromium and 8% nickel austenitic stainless material is commonly selected for general corrosion resistance, clean appearance, and ordinary washdown exposure. Since 1962, Cold Headers has helped distributors, repair teams, and OEM sourcing projects locate specialty socket products.

Technical Highlights

  • Material: 18-8 Stainless Steel
  • Thread Size: 4-40
  • Length (overall - includes head): 1/2 in.
  • Head Style: 82° Countersunk Flat
  • Drive Type: Internal Hex
  • Locking Feature: Nylon insert providing prevailing torque
  • Nylon Insert Diameter (P): 1/16 in.
  • Nylon Insert Location (N): 7/64 in. +/-1/2 pitch
  • Head Dimensions: ASME B18.3

Call 773-775-7900 or email Sales@coldheaders.com for pricing, availability, or a quote.

 		N/A

4-40 x 5/8 18-8 Stainless Steel Flat Head Cap Screw with Nylon Insert is built for a properly cut 82-degree countersink where the head can sit flush or slightly below the surface. A countersunk head bears on the cone rather than a broad underside, so clamp load should not be treated like a full socket head cap screw.

For walk plates, step surfaces, or low-snag equipment panels, confirm countersink geometry, thread engagement, and whether the nylon insert suits the service conditions. For a low-profile head without cutting a countersink, compare 18-8 Button Head Socket Cap Screws with Nylon Insert.

The 18% chromium and 8% nickel austenitic stainless material is commonly selected for general corrosion resistance, clean appearance, and ordinary washdown exposure. Cold Headers can help verify the exact 18-8 flat head nylon-insert configuration before quoting pricing and availability.

Technical Highlights

  • Material: 18-8 Stainless Steel
  • Thread Size: 4-40
  • Length (overall - includes head): 5/8 in.
  • Head Style: 82° Countersunk Flat
  • Drive Type: Internal Hex
  • Locking Feature: Nylon insert providing prevailing torque
  • Nylon Insert Diameter (P): 1/16 in.
  • Nylon Insert Location (N): 7/64 in. +/-1/2 pitch
  • Head Dimensions: ASME B18.3

Call 773-775-7900 or email Sales@coldheaders.com for pricing, availability, or a quote.

 		N/A

4-40 x 3/4 18-8 Stainless Steel Flat Head Cap Screw with Nylon Insert gives buyers an exact overall length for a countersunk screw, not an under-head measurement. A buyer moving from socket head cap screws should remember that flat heads are not measured from under the head. The inch-series flat head angle is 82 degrees; metric flat heads are commonly 90 degrees, so the countersink angle should be checked before substitution.

Typical applications include countersunk hinge hardware, latch plates, and access doors, where nothing proud should catch passing material or hands. For a low-profile head without cutting a countersink, compare 18-8 Button Head Socket Cap Screws with Nylon Insert.

The nylon pellet presses against the mating thread to provide prevailing torque without changing the countersunk head geometry. Cold Headers can handle supported non-catalog pellet-size requests through in-house pelletizing.

Technical Highlights

  • Material: 18-8 Stainless Steel
  • Thread Size: 4-40
  • Length (overall - includes head): 3/4 in.
  • Head Style: 82° Countersunk Flat
  • Drive Type: Internal Hex
  • Locking Feature: Nylon insert providing prevailing torque
  • Nylon Insert Diameter (P): 1/16 in.
  • Nylon Insert Location (N): 7/64 in. +/-1/2 pitch
  • Head Dimensions: ASME B18.3

Call 773-775-7900 or email Sales@coldheaders.com for pricing, availability, or a quote.
Brands N/A Cold Headers, Inc.
Diameter N/A 4-40
Length N/A 1/4 in N/A 3/8 in N/A 1/2 in N/A 5/8 in N/A 3/4 in
Material N/A 18-8 Stainless Steel
Quantity N/A 100
Package Type N/A Box