Heli-Coil inserts are precision formed coils of extremely hard, diamond shaped 304 stainless steel. When installed into an STI tapped hole, they provide permanent conventional 60° internal screw threads. This assembled insert accommodates any standard bolt or screw as per MIL-S-7742 and AS8879 (UNJ controlled root radius).
Heli-Coil inserts are larger in diameter before installation than the tapped hole. During installation the inserting tool applies torque to the tang reducing the diameter of the leading coil permitting it to enter the tapped thread. After installation, each high tensile coil of the insert expands outward with a spring-like action permanently anchoring the insert.
All Heli-Coil Inch Screw-Lock inserts are supplied with a red coloring in accordance with NASM21209.

Notes on Insert Specifications:
1. Nominal length is a computed value and cannot be measured. It is the actual assembled length + 1/2 pitch.
2. The number of coils are counted from the notch.
Unit of Measure


On Hand

N/A {0}

Thread Size

N/A M4 x 0.7


N/A 304 Stainless Steel


N/A Screw-Lock, Coarse


N/A None

Outside Diamater Min.

N/A 5.05 mm

Outside Diamater Max.

N/A 5.60 mm

Q - Nominal Length

N/A 6.00 mm

Number of Coils

N/A 6-1/8

Max. Locking Torque

N/A 0.9 N·m

Min. Locking Torque 15th Cycle

N/A 0.16 N·m

Minor Diameter Min.

N/A 4.15 mm

Minor Diameter Max.

N/A 4.33 mm

Suggested Drill Size - Aluminum

N/A 4.20 mm

Suggested Drill Size - Steel, Magnesium, Plastic

N/A 4.25 mm

F - Minimum Drilling Depth for Plug Taps

N/A 12.20 mm

F - Minimum Drilling Depth for Bottoming Taps

N/A 8.80 mm

N/A IMPORTANT NOTE: When using heat-treated steel screws or stainless steel screws with a Screw-Lock insert, an anti-seize compound MUST be applied to the screw or insert to minimize galling and maximize cycle life. To improve the wear life of the screws in Screw-Lock insert applications, specify Nitronic 60 material, Primer Free II coating, Dry Film Lubricant (Molybdenum Disulfide) or Cadmium plating be applied to the insert.

N/A The minimum drilling depths shown below allow for the following recommended practices:
1. Countersinking the drilled hole to prevent a feather edge at the start of the tapped hole.
2. 3/4 - 1-1/2 pitch of insert "set-down" to allow for maximum production tolerance. Dimensions are shown for both plug and bottoming taps.

(Note: Plug taps M8 and smaller have a male center and the drilled hole depth dimensions allow for this length (one half of the diameter of the holt).
Calculation of dimension "F" is as follows:
For Plug Taps M8 and smaller: F = Insert Nominal Length (Q) + .5 (Bolt Nominal Diameter) + 4P (Tap Chamfer) + 1P (allowance for countersink and maximum insert set-down).
For Plug Taps M10 and larger: F = Insert Nominal Length(Q) + 4P (Tap Chamfer) + 1P (allowance for countersink and maximum insert set-down).
For Bottoming Taps: F = Insert Nominal Length (Q) + 2P (Tap Chamfer) + 1P (allowance for countersink and maximum insert set-down).

N/A The minimum tapping depths (Dimension H) are the Minimum for countersunk holes and an insert set-down of 1-1/2 pitch maximum. The calculation for Dimension “H” is:
H=Insert Nominal Length Q+1P
The tapped hole must be held within the stated pitch diameter limits for the required class of fit for the installed Heli-Coil insert.
When anodize, Iridite or other finishes are used, all tapped hole dimensions must be met after the finishes are applied.
Heli-Coil taps in various types and styles produce holes for Tolerance Classes 4H5H or 3B and 5H or 2B for use in the general range of aluminums, magnesiums, mild steels, free machining stainless steels and other free machining materials. Conventional shop practice and production procedures, speeds, feeds and lubricants should be used in combination with proper fixturing and good tapping machines or tapping heads. The tapped hole must be held within the stated pitch diameter limits for the required Tolerance Class of fit for the installed Heli-Coil insert. For Standard (free running inserts), a tolerance class 5H or 2B is recommended. For Screw- Lock inserts, a tolerance class 4H5H or 3B is recommended in order to develop higher locking torques.

M - Countersink Diameter Min.

N/A 4.70 mm

M - Countersink Diameter Max.

N/A 5.30 mm

Pitch Diameter Min.

N/A 4.46 mm

Pitch Diameter Max. - Class of Fit 4H

N/A 4.51 mm

Pitch Diameter Max. - Class of Fit 5H

N/A 4.53 mm

H - Minimum Tapping Depth

N/A 6.70 mm

Tap Major Diameter Max.

N/A 5.01 mm