What socket size are the spark plugs in the 420a?

[DiamondStarMotors]

1/2 inch is too small. 5/8 slips and so does 16mm.

 

[garrettgoines]

That plug is stripped unless your not getting the socket on correctly. Should be 5/8.

 

[scottyhops]

should be 5/8 like garrett said, take a flash light and look to see if its stripped, if not you might have to push down the socket more, you are you a deep enough socket right?

 

[DiamondStarMotors]

should be 5/8 like garrett said, take a flash light and look to see if its stripped, if not you might have to push down the socket more, you are you a deep enough socket right?

That's what i was thinking, probably not all the way on the plug or the socket it self isn't long enough.