Drill Bit of Chassis Punch for 1/4" NPT

Greetings,

I am modifying my keg mash tun and adding a custom made thermowell that will accept a digital temperature probe. I am using a 1/4" tube compression to 1/4" NPT, where the NPT will pass through the keg wall. The 1/4" NPT outside diameter measures 0.518" on my caliper but an online source says the nominal outside diameter is 0.540".

Question is, should I use a 5/8" (0.625") bit or chassis punch to get through the keg or should I use a 1/2" (0.50") bit/punch and then grind out the hole a bit more using a dremel tool and metal cutting wheel?

Suggestions and advice would be very appreciated.

I'd drill it with a 9/16 bit if you had one.

The difference between .540 and .625 is significant. Drill smaller and grind out.

Thanks for the help! A 9/16 bit may be the ticket.