Technical What size helicoil?

[smart51]

Excuse the separate thread, but what the he'll is going on with these helicoils?

They are supposed to be M14 x 1.25. The pilot drill is marked 14.3 and pretty much is. It fits easily through a helicoil. The tap is about 16mm in diameter, which sounds plausible, but the helicoil itself is 14.3mm ID, compared to 13.7 OD for the spark plug.

Metric bolts are measured in outside diameter, so an M14 thread should be 14mm (if the threads are sharp) and often just under 14mm if they are blunt. The spark plug is right. 14.3mm is the correct pilot hole for an M16 x 1.25, so is correct for the tap. These inserts must be all kinds of wrong.

 

[Toshi 975]

Excuse the separate thread, but what the he'll is going on with these helicoils?

They are supposed to be M14 x 1.25. The pilot drill is marked 14.3 and pretty much is. It fits easily through a helicoil. The tap is about 16mm in diameter, which sounds plausible, but the helicoil itself is 14.3mm ID, compared to 13.7 OD for the spark plug.

Metric bolts are measured in outside diameter, so an M14 thread should be 14mm (if the threads are sharp) and often just under 14mm if they are blunt. The spark plug is right. 14.3mm is the correct pilot hole for an M16 x 1.25, so is correct for the tap. These inserts must be all kinds of wrong.

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The helicoil is basically a coil spring so when inserted the coil is compressed to hold it in place and to give the right dimensions for the thread. Nothing wrong with the bits you have there.