On Apr 14, 5:01*pm, JIMMIE wrote:
What size hole saw do I need to make a hole to mount an old work
octagonal box. Your help will save me time and conversation with
people I had rather not talk with in the BIG BOX store.

Jimmie

I found out something interesting while trying to answer your
question... apparently the Carlon "old work" round boxes aren't UL
listed for fixture support? so I guess they are pretty much only
useful for smoke detectors. Maybe use one with a fixture bar
instead? that is, cut the hole, then install the fixture bar through
the hole (might need a punch to "set" it) then install the box to the
fixture bar. (that's what I did the one time that I had an issue like
this - landlady had a ceiling box "fall down" and I used a fixture bar
and regular box to fix it.)

If you go that route, the size hole saw you need should be obvious
through inspection (that is, take the box and walk over to the hole
saws.)

good luck,

nate