Optional Short kit for 8mm inserts:
not recommended for inserts longer then 8mm, use our standard spark plug kits.

M14x1.25 spark plug thread repair for short 8mm length inserts.
We offer a kit that would have a standard counterbore to create the
countersink for the flange so the insert sits below the surface. The kit
would be used for spark plugs that are NOT recessed. The spark plug
should be visibly near the surface.

Kit p/n 14125F would include 8mm length inserts.
Example: Used in Harley davidson where the spark plug thread
length is 8mm using a Autolite spark plug part number 86
measure your spark plug thread length to be sure.
Many Harley spark plugs use 3/8 and 3/4 reach plugs which would be our
p/n 4412 kit with inserts p/n 44125 for 3/8 and p/n 44111 for 3/4.

Normally a special tool called “seat cut

Standard spark plug kits p/n 4412 or 4412E would not work for short inserts.
See Step #2 found on standard spark plug repair page, the tap must be threaded 1/4″
Below the surface so “seat cutter” can pilot on the shank of the tap. The tap would fall thru
on short threaded spark plug holes so optional kit p/n 14125F is available.
https://time-sert.com/how-to-sp/

Note: Kit p/n 14125D would include 7mm length inserts.