CNC TRUECUT / MACHINING REFERENCE
Wire thread inserts: drill and tap preparation
Plan the drill, STI tap and inspection steps for wire-insert repairs without confusing the receiving thread with the finished screw thread.
Receiving thread versus finished thread
A wire insert leaves an internal thread for the intended screw after installation. The hole machined before installation receives the outside of the insert, so its drill and tap are not the ordinary drill and tap for that screw. An STI tap is designed for this receiving thread. Specify the complete insert system before preparing the hole.
Start with the insert supplier’s data
Confirm nominal size, pitch, insert length, material, locking style and any installation requirements. Use the supplier’s drill, countersink, tap and gauge recommendations for that exact system. A tool sold for another insert system or a generic oversize thread may not satisfy the specified installation.
Depth and clearance
A blind hole needs room for the full usable thread, tap lead, drill point, insert position and installation tooling. The drill point tool can calculate ideal cone height, but it does not determine the insert’s required clearance. Check those allowances in the installation instructions.
Verification and sources
Inspect the receiving thread before installing an insert and verify the finished thread by the method on the drawing. OSG publishes an STI tap drill chart. Confirm it applies to your required insert system and application; the chart is a source link, not a reproduction of proprietary data.