Buying 90 or 82 zero flute counter sinks.

[davidcarmichael]

I have seen it explained that metric screws are 90 degree, inch are 82.

My experience has been that American screws are 82 degrees but all others on the planet are 90 and have been long before metric came along (e.g. UK fasteners). Never used an 82 while in the UK for 30 years (no metric).

 

[Winegrower]

but all others on the planet are 90 and have been long before metric came along

As noted above, aircraft hardware is a 100 degree countersink. Since the Wright brothers, I suppose.

 

[Aukai]

Somewhere in my mind Howard Hughes used flush rivets to smooth out air flow for better aerodynamics on planes. I wonder if he had a hand in this too?

 

[COMachinist]

Well, looks like 82, and 90 would do. I don't work on, or any thing with aircraft. I do use a metric screw once in a great while, but not often. My old multi flute counter sinks chatter like a flock of Magpies.
Any way I did order both sets.
Thank a lot for all the info and help.
CH

 

[pontiac428]

I may not work on (full-scale) aircraft, but I have to do sheet metal every now and again, such as race car aero. I don't own a 100-degree countersink, so when I do countersunk rivets I grab what I have. It works, but it's not as flush as airframe work. Now I now why!

 

[DavidR8]

Go with the 100 deg sinks John, you'll pick up tenths/add top-end/increase fuel economy/look cooler

 

[ddickey]

Well Mike, if ya got lots of extra money to burn, you could always buy one of these!

View attachment 361977

Rohm MT3 is less than $400