Sex bolt indeed!
The plow bolt is the right idea--basically a kind of flat-head
carriage bolt. But way too big. I'm looking for 10-32/24 or 1/4-20.
The real round-head analogy to the flat head would be "mail box
screws." Anyone remember those? :)
But it looks like slotless flat heads (for security purposes) are
not such a common item. So maybe I'll get brass flat heads and turn them
down--this will also give me a smaller "reveal", and look perty nice, as
formerly Droll Troll
There are also "Elevator Bolts" that have a flat head about 1/16" -
3/32" thick - think a "Carriage Bolt" with the same square shank
underhead, but with a flat head instead of a round head.
Used to secure the plywood interior car wall panels to the steel car
frame of an elevator, where the flat head can be hidden in a shallow
drilled recess in the plywood. This leaves a perfectly flat surface
that can be covered with plastic laminate, or a zillion other interior
I use a screw similar to these to hold the bed on the miniature runner sleds
I make.(see them here:
) I happened to get these
from an estate auction of an electrician. The box is marked Greenlee and are
I believe used to hold mounting panels inside electrical boxes. Under the
head of these 10-32 X 3/8" screws there are serrations to keep the screw
from turning. I haven't found a source for them but will need to soon as I
am almost out.
These arn'te completely slotless, but they only have two small holes for
a special spanner:
(You'll have to splice this back together)
Alternatively, go to
& search for flat head
"Tamper-Resistant Drilled Spanner" drive screws.
What size does he need? I find, listed in _Machinery's
Handbook_, (25th edition), on page 1433 (American National Standard
Step and 114 degree countersunk square neck bolts), something which fits
your description, other than having a square projection from the bottom
of the head to prevent rotation as you tighten a nut on it.
It is shown in sizes from #10 through 3/4", so if that would fit
your needs, including the square anti-rotation shank, I think that you
have a name (114 degree countersunk square neck bolt).
I have seen smaller ones, with a spline on the neck, so they
could be pressed into a countersunk hole and act as studs.
Note that also, in a recently posted URL
I find flatheads with two small holes (marked "Drilled Spanner"), and
two notches from the edges which do not meet in the center (marked
"Notched Spanner"), which might also fit your needs -- which are
somewhat losely specified, unless you have more detail in another branch
of the thread which I have not yet visited.
Fasteners like this are commonly used on aircraft. The "nut" wrenching
element will snap off at a certain torque level leaving a smooth round
collar. Standard nuts (fine thread) can be used as well. The bolt is
held against the nut wrenching torque by an allen wrench in the hex recess
in the shank.
Slotless flathead machine screws are widely used on farm machinery,
specifically for attaching plowshares and cultivator shovels. They are held
against nut tightening torque by a square shank under the head, similar to a
carriage bolt. These bolts are not particularly expensive and may be bought by
the each in most farm supply stores. They will be in larger sizes, from 3/8"
and up, and will probably have coarse threads.
No, that's really what a slotless flat head screw in 10-32 or 10-24 or 1/4 - 20
is called. It's called a sex bolt, MSC sells them at mscdirect.com and you buy
them with matching *round head* slotless mating nuts. In operation it's a lot
like a paper clamp screw for binding paper with holes drilled in it.
These *are* a security item. For permanent assemblies.
I love: Dona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.
I drive: A double-step Thunderbolt with 657% range.
I fight terrorism by: Using less gasoline.
There are also tamper proof screws that are slotless
and without spanner holes. They have a very slightly
oval shaped head that will engage a mating driver.
They aren't cheap, but work quite well and look nice.