what size drill bit

[tattoo]

I have some grease nipples that says 6mm on the pkt..is this the size of the threads, if so is it a 6mm drill bit to drill the hole to tap threads into...I'm embarrassed to say that I've never had to do jobs like this so I haven't a clue which size drill bit goes to which size tap

[simo]

No you would need a smaller drill. Would have to look in my Zouce book when I get home . It also depends on the pitch of thread ( course or fine) . Will let you know if there's no other replys.

[silver storm]

I have tapped 6mm thread after using a 5mm drill bit and had no problems with the thread.
Stevie

[silver storm]

I have tapped 6mm thread after using a 5mm drill bit and had no problems with the thread if it is the standard 6mm it will have a fine 1.00 thread.
Stevie

[tattoo]

Thanks for the replies...I think I have it wrong, I've been out n tried a socket on the nipple and that's 6mm so the threaded part will be smaller..really wish the packet had more imfo on it other than just 6mm

[MacV2]

You can check the thread size of the nipple by using the die's in the tap & die set, try a 5mm to start & if it does not wind in freely stop & try a size either side of 5mm...Then use the equivalent Tap to thread the hole.

[edds11]

use macs method but I think its 6mm nut, 4mm thread 3mm drill.

[simo]

Aye,5mm drill for 6mm thread.

[tattoo]

Thanks for the replies, I'll do some test hole on a piece of alloy I have before doing the attempting it on the part

[bigtwinthing]

Just be careful, some nipples look like they have a thread but in fact they are just like a ridge around the nipple and they just are lightly banged in after drilling the correct hole. they generally dont fall out either if the right size hole is drilled.i can photo you one to show you.

[spikenipple]

The Metric thread system is an easy one to work out. If you know the pitch (distance between peaks of the thread) of the thread which you are tapping, you simply remove this number from the thread size (eg M6=6mm) to find your tapping drill size.

For example

M6 (nominal diameter) x1mm (pitch) = 6-1= 5mm tapping drill
M8x1.25mm = 8-1.25 = 6.75mm (6.8mm is the common size) tapping drill
M10x1.5mm = 10-1.5 = 8.5mm tapping drill

etc etc

If your grease nipple is an M4 thread (which is 4x0.7mm) then drill it with a 3.3mm drill, otherwise you will have a bloody hard time tapping it and are likely to either break the tap or end up with a terrible thread form.