There's been a lot of different plugs in them over the years

Mine had a Champion RDJ7Y taper seat plug but some of them have gasket seat plugs. Actually they will interchange on the engine as I have ran both. There wasn't any rpm difference

The gasket plug would be a CJ instead of a DJ The DJ is.325 reach and the CJ is 3/8" reach

Make sure you have the resistor (R) plug or there'll be radio problems

The "Y" is a projected tip

The threads are 14mm