Hi Ian, info that I found for the KLG ML50
"Long reach 18mm spark plugs
Insulator made by Alumina (Al2O3)
Heat range adjusted to 190 +/- 10% imeps.
(171 to 209)
Spark plugs would be Ni-Cr quality
Additional Information
SKU 1522
Manufacturer KLG
Part Number ML50
Diameter 18mm
Reach 19mm (3/4")
Hex Size 25.4mm (1")
Seal Type Gasket Seat
Resistor No
Terminal Type M4 Thread
Electrode Material Standard Nickel
Projection Type Non Projected
Tip Configuration Single Electrod