Robertson Square Drive

NW Modeling List nw-modeling-list at
Mon Nov 1 13:07:50 EDT 2010

Actually, boys, the drywalls screws are the weakest of the screw types in
general use. They are made specifically for the attachment of drywall to
wood studs or the thin C-section metal studs used in partition walls. They
also are specified to have a BUGLE head which really only has the volume to
hold a Phillips-type socket. The bugle head is made to 'sink' into the
paper and gypsum without tearing the paper. The screws have the minimum of
corrosion resistance in the black or gray phosphate coating and they have
the lowest strength possible by using a very low alloy steel and a very thin
case hardness.

The Robertson drives are usually used in screws that require higher strength
or more drive torque- the square drive does not cam-out like the Phillips
drives do. McFeely's sells to mainly wood construction, but there is a
whole family of square drive screws used for cold-formed steel construction
in load bearing connections- See Grabber or Buildex for some of these
screws. There are some other drive sockets used that are similar to TORX
type sockets in these screws.

In general, the wood screws with 82 or 90 degree countersink heads will
require predrilled and countersunk pilot holes. (Use a combination drill and
c'sink.) Bugle heads in lower density woods like white pine will mostly
sink in flush, but will not in yellow pine or fir especially if they have
dried out for a while; the wood will be too hard.

If you cannot find square drive tips at Lowe's or Home Depot ( not
untypical) go to the 'professional' stores especially those aimed at the
commercial construction market as commercial construction doesn't use wood
that much, but does use a lot more cold-formed steel and square drive
screws. Look for Fastenal, Grabber, White Cap or HILTI. Also these guys
will have long drive bits used in tools using collated screws ( screws in
long plastic strips for feeding automatically) to gain access into cramped

Gary Rolih

A screw guy in Cincinnati

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