Silicone Thread Plugs Ø 6 to 28 mm

Silicone Thread Plugs for Powder Coating

Powder or liquid paint inside internal threads wastes valuable time post-cure: bolts bind, threads require chasing with a tap, and fresh coating near the rim frequently chips off. These silicone thread plugs seal internal threads across their full length prior to coating. They maintain dimensional stability in curing ovens up to 315 °C and are recommended by the manufacturer for liquid paint, e-coating (KTL), anodizing, and electroplating as well.

Important distinction: plastic thread plugs sold as end caps for furniture tubing, square tubing, or chair legs will melt in the curing oven. Our plugs are pure masking products engineered specifically for surface finishing technology. Find all other silicone plugs in our collection of silicone plugs for bores and threads, and view surface masking supplies under masking products.

How Thread Plugs Work in Powder Coating

The silicone thread plug features a slight taper with a pull tab at the head. Over its length of 25.4 mm, it tapers by only about 2 mm. As you twist it into place, the soft silicone conforms directly to the thread flanks, ensuring a tight seal that protects the internal turns themselves, not just the opening.

These plugs intentionally omit a flange, leaving the surrounding surface clear so powder can coat right up to the thread edge. Models from M12-14 upward feature a hollow core design, allowing them to be inverted and slipped over short threaded studs when needed.

Thread Plug, Ribbed Plug, or Tapered Plug?

• Threads that must stay completely clean: Thread plugs. They are the ideal choice for load-bearing bolted joints and production runs with uniform thread sizes from M6 to M27.
• Multiple varying thread sizes on a single component: A silicone ribbed plug with stepped rings covers multiple dimensions from M4 to M18, saving sorting effort.
• Smooth bores without threads: Use our small tapered silicone plugs for non-threaded holes.
• Protecting threads during abrasive blasting: Standard silicone is not blast-resistant. In the blast cabinet, use tapered EPDM rubber plugs and swap them for silicone thread plugs prior to oven curing.
• External threads and studs: Slip silicone caps over these features.

Application Examples for Threads M6 to M27

M6 to M10: Motorcycles, Automotive, and Bicycle Accessories

License plate holders, fairing brackets, footpeg mounts, and handlebar clamps almost exclusively use M6, M8, or M10 threads. The two smallest thread plug sizes cover these dimensions seamlessly.

M12 to M16: Wheel Hubs and Suspension Assemblies

Wheel hubs feature lug bolt threads in M12x1.5 or M14x1.5. When coating hubs or brake caliper brackets, every single thread turn must remain free of paint to ensure lug bolts achieve their required clamping force at specified torque values. Select your plug based on nominal thread diameter; fine-thread pitch does not alter sizing.

M18 to M27: Frames, Hydraulics, and Structural Steel

Weld nuts on trailer frames, hydraulic cylinder ports, and threaded connections in structural steel base plates typically fall between M18 and M27. Thread chasing in these large sizes is costly and time-consuming because large-diameter taps are rarely readily available.

Size Chart for Silicone Thread Plugs

Select the model whose range includes the nominal diameter of your thread. If your thread size falls right on the boundary between two models, the smaller plug provides a tighter seal, while the larger plug is easier to twist in.

Practical Guidelines for Masking Internal Threads

• Allow air to escape from blind holes. Do not press the plug all the way to the bottom of a blind hole. Trapped air expands inside the oven and can force the plug out. Twist it in slowly, leaving a small air gap at the bottom.
• Mask clean threads only. Residual cutting fluid or oil inside threads outgasses during heat curing, causing pinholes and cratering around the opening. Degrease all threads prior to masking.
• Verify threads post-cure. A matching bolt should thread in smoothly by hand all the way to the bottom. If it turns freely, the masking seal was complete.
• Pull out using the tab. After curing, grasp the plug by its tab and twist counterclockwise while pulling. This breaks the seal along the thread turns without tearing or lifting the fresh coating edge.

Learn more about surface pre-treatment and where masking fits into the coating process in our

powder coating guide magazine article.

Specifications & Features

• Heat-resistant solid silicone, rated for curing temperatures up to 315 °C
• Tapered profile with pull tab and flangeless design, 25.4 mm length; hollow core from M12-14 upward
• 9 distinct models designed for internal metric threads from M6 to M27 (including fine-pitch threads)
• Color coding: M6-8 black, M8-10 brown, M12-14 to M26-28 white
• Reusable as long as the silicone retains its elasticity
• Available package sizes: 10, 25, or 50 pieces

Frequently Asked Questions

Can I use standard plastic thread plugs intended for furniture or general hardware?

Not in a powder coating oven. Commercial plastic end caps are typically molded from PE, PP, or PVC. At 180 to 200 °C, they deform or melt directly into the thread turns and degrading PVC releases corrosive vapors inside your oven. Our silicone plugs are purpose-built industrial masking products designed for easy removal after heat exposure.

Which plug size fits an M12x1.5 thread?

Base your selection on the nominal thread diameter, in this case, 12 mm. Choose model M12-14. This rule applies to all metric fine threads: an M14x1.5 thread fits either M12-14 or M14-16, depending on desired plug fit tightness.

Does the plug protect deep internal threads?

Yes. The plug fills the first 25.4 mm of thread depth and seals off the entry bore. Powder coating particles cannot penetrate past the sealed zone to reach deeper thread turns.