Thread Repair Workshop Kit UNF 1/4 – UNF 1/2

• The kit is used to repair worn, stripped or damaged internal threads in metallic and many other load-bearing materials.
• It is also suitable for permanent thread reinforcement when the base material has lower shear strength and the connection needs to be permanently load-bearing.
• Thanks to the coordinated interaction of spiral drill, STI tap, installation tool, tang breaker and thread insert, the repair process can be carried out systematically.
• The free-running V-COIL system is useful when the repaired internal thread must remain reliably usable for standard screw connections.
• Process: manual or assisted drive depending on your tool holder and machine configuration.
• Use: thread cutting, re-tapping and thread cleaning depending on the condition of the thread.

Note When selecting the kit, make sure that the thread system and thread design of the component clearly match the included UNF repair range and that all work steps are carried out in alignment with the existing hole.

• Coordinated repair kit for multiple UNF sizes in one set.
• Suitable for restoring load-bearing internal threads after damage or wear.
• Thread inserts made of stainless steel support a wear-resistant and corrosion-resistant thread solution.
• STI taps and installation tools are matched to the installation of the thread inserts.
• Useful for workshop, maintenance, assembly and component refurbishment.
• Can reduce scrap if damaged threads are repaired instead of replaced.

• A precise workflow is required for a clean repair, as alignment errors can impair thread quality.
• The kit is designed for the included UNF ranges and does not replace a universal solution for deviating thread systems or special applications. For those cases, see our threading tools.

1. Inspect the damaged internal thread and assign the component to the appropriate UNF version from the kit. Align the workpiece so that all machining steps are carried out cleanly in line with the axis of the existing hole.
2. Select the correct spiral drill and drill out the old thread in a controlled manner. Then clean the hole thoroughly so that the receiving thread can be produced cleanly.
3. Position the matching STI tap and cut the receiving thread in alignment. Use a suitable cutting medium and guide the tool in a controlled way.
4. Place the matching V-COIL thread insert onto the manual installation tool and screw it evenly into the prepared receiving thread. Position the insert so that the thread function in the component is professionally restored.
5. After installation, remove the driving tang using the appropriate tang breaker and check the finished thread for proper seating and function. This ensures that the repaired connection can be used reliably.

• 5 STI single-pass taps, Form D, HSS-G
  • 1 piece VÖLKEL 03155
  • 1 piece VÖLKEL 03156
  • 1 piece VÖLKEL 03157
  • 1 piece VÖLKEL 03158
  • 1 piece VÖLKEL 03159
• 5 tang breakers
  • 1 piece VÖLKEL 07009
  • 1 piece VÖLKEL 07011
  • 1 piece VÖLKEL 07013
  • 1 piece VÖLKEL 07014
  • 1 piece VÖLKEL 07015
• 5 manual installation tools with locking ring
  • 1 piece VÖLKEL 08009
  • 1 piece VÖLKEL 08011
  • 1 piece VÖLKEL 08013
  • 1 piece VÖLKEL 08014
  • 1 piece VÖLKEL 08015
• 95 thread inserts type S free-running length 1.5 D
  • 25 pieces UNF 1/4" x 28
  • 25 pieces UNF 5/16" x 24
  • 25 pieces UNF 3/8" x 24
  • 10 pieces UNF 7/16" x 20
  • 10 pieces UNF 1/2" x 20
• 5 STI spiral drills
  • 1 piece 6.7 mm
  • 1 piece 8.3 mm
  • 1 piece 9.8 mm
  • 1 piece 11.5 mm
  • 1 piece 13.0 mm

• Product type: Thread repair kit
• System: V-COIL
• Thread system: UNF
• Thread type: Internal thread repair with wire thread inserts
• Repair range: 1/4" to 1/2"
• Thread insert type: Type S free-running
• Insert length: 1.5 D
• Material of thread inserts: Stainless steel
• Included taps: STI single-pass taps Form D
• Tap design: HSS-G
• Additional components: Manual installation tools with locking ring, tang breakers and STI spiral drills

What is this kit intended for?
This kit is designed for repairing and reinforcing damaged UNF internal threads. It combines the required machining and installation tools in one coordinated set.

What does UNF mean for this product?
UNF stands for Unified National Fine and designates an inch fine thread. Compared to coarser series, it is often used wherever a finer thread pitch and a precise screw connection are required.

Why are STI taps required?
STI taps create the special receiving thread for the thread insert. They are therefore a central part of thread repair and technically belong to thread repair, not to the normal reworking of a standard thread.

What is the purpose of the thread insert?
The thread insert restores the thread function in the component and can additionally stabilize the connection in softer base materials. Thanks to the metallic insert structure, the screw connection remains durably usable.

Is this kit only suitable for repairs?
No, it can also be used for targeted thread reinforcement. This is especially useful when components are repeatedly screwed together or when the base material is more sensitive to thread wear.

What should I pay particular attention to during use?
Proper alignment, the correct matching of the components within the kit and controlled installation of the thread insert are essential. Only then can a load-bearing and functionally reliable thread repair be achieved.

Where can I find further information about this product type?
VÖLKEL catalog as PDF