Last time when I was in NS BVeh Mechanic, people just tighten spark plug with wrench.
Where got so hard, 17/18 yo ah beng can do it.
One of the most changed parts. The wiper and alternator also change alot.
You tighten until cannot easily tighten anymore, then go another quarter turn can liao.
Only scare is overtighten and strip, you will feel it one, it slips and slides.
My copper compression fittings i DIY at home, done in the same way.
30 years hot and cold water going through with thermal and cold water expansion, still not leaking.
I see most of the JHK workshops also don't care one.
Even if they use a torque wrench, don't know how accurate is it or has it been regularly calibrated/tested or not.