Section 07 / Inserts

A stripped thread is a tap size away from fixed.

Helical thread inserts and rivet nuts, for the two jobs where the base material cannot hold a thread on its own: soft aluminum and cast housings that strip, and thin sheet that has nothing to tap into. Stainless wire inserts in three lengths with the STI taps that cut their holes, and flanged rivet nuts in steel and aluminum.

304 stainless wire 1D, 1.5D, 2D Rivet nuts #6 to 3/8 in

MOD 07 / Price basisWritten quote

Wire inserts: Per pack of 25 or 100
STI taps: Per each
Rivet nuts: Per box of 100

Quoted against your inquiry and confirmed in writing. A repair job of 10 inserts usually means one pack of 25 and one tap.

Stainless helical thread inserts beside a tap and an aluminum block with one installed — The tap is oversize on purpose. An STI 1/4-20 tap cuts a hole the insert coils into, leaving a standard 1/4-20 thread inside.

Line 07.1 / Helical wire inserts

Helical wire thread inserts

A diamond-section coil of 304 stainless wire. You drill out the damaged hole, tap it with the STI tap for that size, wind the insert in with the install tool, and break off the tang. The finished hole takes the original screw. Stainless threads in an aluminum casting outlast the casting's own threads many times over, which is why people specify them in new work too, not just repairs.

Length is called out as a multiple of diameter. 1D is the insert as long as the screw is wide, 1.5D and 2D go deeper. In aluminum, go 2D wherever the hole is deep enough and never shorter than 1.5D. Our rule for thread engagement in aluminum is twice the screw diameter, and a 1D insert in a deep hole leaves the screw carrying load on the soft threads below it.

What breaks most installs: drilling with the wrong size before the STI tap. The STI tap drill is bigger than the standard tap drill. Use the number in the table below, not the one on the drill index you normally reach for.

Material: 304 stainless, tanged
Inch sizes: #4-40 to 1/2-13 UNC, common UNF
Metric: M3 to M12 coarse
Lengths: 1D, 1.5D, 2D
Tools: STI taps per size; install and tang break tools on request
Price basis: Per pack of 25 or 100; taps per each

Flanged rivet nuts, one installed in thin aluminum sheet — The installed one has collapsed behind the sheet into a bulge. That bulge is the clamp.

Line 07.2 / Rivet nuts

Rivet nuts for thin sheet

A threaded sleeve that sets like a blind rivet. You drill one hole, push the rivet nut in, and the tool pulls the thread toward you so the body buckles behind the sheet. Now 18 gauge steel or 0.063 aluminum has a real thread in it, reachable from one side. Panels, enclosures, tube frames, roof racks.

We stock flanged rivet nuts in zinc-plated steel and in aluminum. Steel for steel sheet and higher clamp loads, aluminum for aluminum sheet and anywhere weight matters. Grip range matters here too: each size covers a band of sheet thickness and the reply will name the one that fits your sheet.

Spinning in the hole is the classic failure. It comes from an oversize hole or an under-set nut. Drill to the exact size in the table and set until the tool stops, not until it feels tight.

Material: Zinc-plated steel; aluminum
Inch sizes: #6-32 to 3/8-16
Metric: M4 to M10
Head: Flat flange
Price basis: Per box of 100

Tap and drill sizes

MOD 07 / Hole data

Helical wire inserts, STI tap drill. Standard values for common inch and metric sizes.
Thread	STI tap	STI tap drill	Standard tap drill, for comparison
#8-32	STI 8-32	11/64 in	#29
#10-24	STI 10-24	13/64 in	#25
1/4-20	STI 1/4-20	17/64 in	#7
5/16-18	STI 5/16-18	Q (0.332 in)	F
3/8-16	STI 3/8-16	X (0.397 in)	5/16 in
M6×1.0	STI M6	6.3 mm	5.0 mm
M8×1.25	STI M8	8.4 mm	6.8 mm

Flanged rivet nuts, round body. Hole size from the common published values; confirm against the box.
Thread	Hole	Typical grip band
#8-32	0.257 in (F)	0.020 to 0.080 in
#10-24	0.257 in (F)	0.020 to 0.080 in
1/4-20	0.390 in	0.027 to 0.165 in
5/16-18	0.468 in	0.027 to 0.165 in
M6	9.0 mm	0.5 to 3.0 mm

Install notes from the counter

Note 01

Go/no-go the STI hole

An STI plug gauge confirms the tapped hole before the insert goes in. Cheaper than backing out a mangled coil.

Note 02

Wind it 1/4 to 1/2 turn below the face

An insert flush with the face loses its top coil. Set it just under.

Note 03

Leave room for the broken tang

In a through hole the tang drops out the far side. In a blind hole it falls to the bottom, so drill at least one thread pitch deeper than the insert length.

Note 04

Stainless screws gall in stainless coils

Use a dab of anti-seize on 18-8 screws going into a wire insert. A seized screw tears the coil out with it.

Who these suit, and who they do not

Mostly maintenance techs fixing stripped holes in pump housings and gearbox covers. Fab shops come in for rivet nuts when a panel in 16 gauge needs a thread, and prototype builders put stainless coils into 6061 from day one so the first teardown does not wreck the part.

Not for: anyone who needs a keyed or key-locking insert, a press-in self-clinching nut, or install tooling for a production line. We sell the insert, the tap and the simple hand tools. Production setting equipment is outside what the counter carries.

Inquiry lineWhat to send

Thread size, insert length (1D, 1.5D or 2D), quantity, and whether you need the tap. For rivet nuts: thread, material, sheet thickness and count.

Send a parts list

One pack.One matching tap.

Name the thread and the length. The written reply pairs the insert with the right STI tap and drill.