What type of screw is this?

Hi,
I am restoring a cast iron letter embosser and i have come across a screw head i have not seen before, similar to a modern spanner bit , however one hole is square and one is round. I am assuming this needs to be removed as there must be a spring under it, please see photos attached, thanks

 

Tamper proof screw. Although I dont recall ever seeing one with one square and one round hole (Typically 2 round holes)

 

If you need to remove it, use a good rust penetrant like PB Blaster, tap repeatedly on screw to aid penetration, then wait a day. Take a cheap blade screwdriver with a blade width that will turn in the space available. Grind or file off the middle of the blade so all that's left are two nubs that fit into the screw's holes. Insert and turn ccw.

 

Screw is that way to keep users from disturbing a "factory setting" of the proper spring tension. In US Navy training schools, any screw with a setting which sailors were not to disturb was deemed a "DFW" screw, for "Don't F--- With."

 

Well if you are restoring it then you should have the ability to make a spanner wrench (?) to fit that screw seeing you might need more torque to get it out.

 

Ha!!!!!
THAT explains it fully!

 

You can buy a set of bits for security screws.
Even the double round might work if the pins are the correct diameter and distance apart.
Still watch it if there's a spring!

 

Thanks guys, this is bigger than a standard tamper screw, the space between these holes is at least 12mm, my first thought was this is to stop someone opening it with the tension of the spring, but i dont think ill be able to clean the metal around the top stamp holder with out removing this - although i am in Ireland i think it may be British made between 1890-1910 but so far i have only seen one picture of a similar model for sale on ebay > http://www.ebay.co.uk/itm/Vintage-E...280114?hash=item1c7b556c32:g:g4MAAOSwA3dYiw9g

it differs from others in that it has two piston style rods on the external of the spring assembly , which have flathead screw heads on the top but have tried and failed to turn these even using release sprays and time

i will try work around this for now, as 80% of the paint on mine is missing i was going to polish the cast iron to a mirror finish which seems to work beautifully on the parts i tested

 

The things one learns!
I had no idea there even was such a thing.

 

Try some heat from a propane torch!

 

The 3 things that release stuck ferrous parts are penetrants, heat, and impact/vibration, best if used in combination. The heat and impact causes tiny changes in the area of contact, allowing the penetrant to creep in. I heat things until the penetrant I've applied starts to smoke, then let it cool while subjecting it to impact. Most hammer drills are good for applying the needed vibration/impact.

 

And Spring would probably know about old stuff with springs. That looks like more work than it's worth, unless you have a use for the gizmo. Some modern machinery simply won't cut the mustard when dealing with antique metal whatsits.

 

Would love to see the finished product, especially as you are polishing the cast iron.
I would think it will look quite handsome once you have completed it.

 

Nono, it looks like it had shiny black enamel on it when new, I think it would be best to put it back that way, or make it two-tone, maybe gloss black with a red or gold handle. But it isn't mine.