OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Honda Engines Yard King 125cc Briggs 450-series which spark plug?

Yes the A7TC is 10mm x 1mm, Thread Range: 12.7mm BriggsHandy

You don't need to worry about the plug length being longer than the hole ,I've had mower spark plugs
last 10 years ,the Briggs motors can look barely used in 7 years and are completely worn out blowing smoke
like the one below ( Oil still looked new) ,I checked a 500E and 550EX and both have the last threads black .

After all they are only cheaply made motors.