it sux major a$$ drilling more than 6mm dia; and that is in that stoopid brass. i would strongly advise you try to drill like this:
3.5
5.5
6
7
8
9
10
11
12
i did it
3.5
5.5
6
8
this sucked alot
10
this sucked real monkey nuts, thought my machine was gonna vibrate to hell, took 30mins for just the last step
12
so for a 1/4NPT u need a 12mm drill and the right tap ofcourse (the tap is gonna cost u though, mine was about 70€ for just the tap)
i found this really cool DIY shop where they have EVERYTHING; my parents tell me they are of a duying breed. brother of 60 with his 2 sisters. 20 allen bolts, m4 , no problem, in stock. 3.3mm drill bit! no problem in stock. 1/4npt tap, no problem, in stock.
i also bought a raco brand universal tap kit for 20€ everithing upto m12. those taps look a bit more crappy than the expensive one though.
the tapping in itself is a piece of cake!!! and it is really cool, the metal makes this nice screeching sound while you scrape away the thread. i didn't even have the right handle to work that large tap, just used a adjustable wrench (imagine); and even then i still didn't fux0r it up. just take it slow (u could go real fast, but they say it generates alot of heat even at the handspeed rpm), and u will be fine. in the shop they confirmed that for m4 u need 3.3drill with m4 tap.
anyway, my hose barb screws in like butter (cost me 1hr to get there though) could have been faster by using more drills to get to 12.
hope this clears it out some.
cheers m8
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