You can drill a pilot hole, but if you get the hex-head screws that have a
very sharp point, you can drive them using a cordless drill (or corded, it's
just that most people seem to use the battery stuff these days). They will
spin against the metal for a short time and then bite in. That is in fact
what most people do. If you want to use screws with a phillips head, you
will have to drill a pilot hole.

Actually both the drill and the "zip" screws bend the pipe somewhat, but it
springs back.

Sheet metal screws are self tapping, in a sense, but most of them are not
really self-drilling. These special sharp screws work ok with fairly light
material like ductwork.


"Joe Odom" wrote in message
...
I need to replace the vent pipes for my hot water heater and furnace-
they're 3", 4" and 6"diameter and made of sheet metal. The duct assembly
is
held together with short sheet metal screws-- and I'm not sure how to
start
the screws in the new vent system.

I always thought sheet metal screws were self-tapping but doesn't seem
like
you could push very hard to self-tap without bending or crushing the pipe-
especially the large diameter ones. Do I need to drill a pilot hole or
what?

Joe

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