On Thu, 21 Aug 2008 00:37:52 -0700 (PDT), wrote:

But how do you know the right "size" - my general rule of thumb is to
stick a PZ2 in (providing its a PZ screw),

Most "normal range" PZ screws are PZ2. Big ones say from No.10 (No.12?)
and up are PZ3. PZ1 from No.4 down?

The fit of the bit into a PZ head is fairly positive provided the driver
and head are not baddly worn. The point of the driver should fit flush
with the head not disappear into it (PZ1 or 2 into PZ3) or sit proud (PZ3
into PZ2 or 2 into 1).

--
Cheers
Dave.