what size drill bit

To be a 7 they must be very old. Are you sure they are not

If they are 7's then a 5mm drill in a soft wall (breezeblock etc) or 5.5mm in a hard wall e.g. brick.

Google is your friend.......

Suggest you start with a smaller bit than you think is necessary, and also try initially without hammer action in case you found a soft bit of wall like a mortar joint. (Don't persist without hammer action if the wall is hard, as you'll overheat the bit.)

In some types of wall, the hole easily ends up wider than the bit, and your smaller bit might actually have created the right size hole. However, if the hole needs widening, you can now do this with the right bit, and hammer action won't be required, so the hole will be a cleaner cut and stronger.

In airated thermal concrete blocks, never use hammer action (it causes significant damage in the structure around the hole), and even masonary bits are not a good idea (once you've gone through the plaster). For these, you want an accurate parallel sided hole. I use old HSS bits, but don't expect the bits to last. Again, the two bit method can work very well.

"Andrew Gabriel" wrote in message news:lctc69$i4l$ snipped-for-privacy@dont-email.me...

Er, excuse me, but isn't that just an expansion of exactly what I said it two lines?