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4-40 Countersink size?

LettersFromFlyoverCountry

Well Known Member
What size countersink cutter for the 4-40 screw callout in Section 42 page 1?

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I don't seem to see it listed on the Van's RV-12is list of recommended tools.

And thank you.
 
Last edited:
If the screws originated from an aviation supply place, they will be 100 degree countersinks. Practice using your micro stop countersink on some scrap until you get the depth setting dialed in
 
AN507 or MS24693 screws are 100* head angle. The "D" dimension of the head diameter to the sharp points is .207/.225".
 
Just to follow up, a 4-40 takes a #43 bit for the hole so there's nothing that will fit in a microstop countersink cage as far I could find online for countersink cutters. I guess enlarging the hole to a #40 is the only way to do this.
 
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