Standard to metric

[Joat]

I need some standoffs, but they seem to only offer then length I need in standard, so the plan is to buy the standard ones and bore and tap them to metric , m3x.5mm so the ? is what size standard do I need to give me enough meat to bore and tap to metric? 2-56, 4-40, 6-32 ? I dont have standard hardware so I have no idea how it compares to metric.
T.I.A

[rex cars]

2-56 will leave enough meat for you to drill and tap to m3.

[KBrog]

4-40 would be closer. Its just under 3mm. Here the tap and drill sizes. Hope this helps.

--Tap---------Drill
2.0mm-------.0619
2-56---------.0669
2.5mm-------.0776
4.40---------.0888
3.0mm-------.0978
6-32---------.1055--(#36)
4.0mm-------.1300
8-32---------.1349--(#29)
10-32--------.1587--(#21)
5.0mm-------.1637

[C*H*U*D]

I think he's talking about drilling out standard threads.....not just opening up an existing hole (correct??). If you run a .098" drill into a tapped 4-40 hole, you will still leave behind threads, where you want strong material to be.

McMaster has metric standoffs in hex shape if that helps:

http://www.mcmaster.com/#catalog/115/3214/=58jiy8

.

[Joat]

Originally Posted by rex cars

2-56 will leave enough meat for you to drill and tap to m3.

thanks

Originally Posted by KBrog

4-40 would be closer. Its just under 3mm. Here the tap and drill sizes. Hope this helps.
thanks
--Tap---------Drill
2.0mm-------.0619
2-56---------.0669
2.5mm-------.0776
4.40---------.0888
3.0mm-------.0978
6-32---------.1055--(#36)
4.0mm-------.1300
8-32---------.1349--(#29)
10-32--------.1587--(#21)
5.0mm-------.1637

Thanks

Originally Posted by C*H*U*D

I think he's talking about drilling out standard threads.....not just opening up an existing hole (correct??). If you run a .098" drill into a tapped 4-40 hole, you will still leave behind threads, where you want strong material to be.

McMaster has metric standoffs in hex shape if that helps:

http://www.mcmaster.com/#catalog/115/3214/=58jiy8

.

Yes you are correct, should have explained better, but you got it right on the button, sadly mcmaster rapes people on shipping that arent in the 48,but thanks for the heads up

[C*H*U*D]

A 4-40 will have threads out to about .113". An M3 needs to have threads out to about .115", so drilling out a 4-40 would leave you with barely enough material for the screw to grab. I think Rex is right.....a 2-56 standoff would be better.