replace screws with carriage bolts

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carriage bolt


This trick defeats a thief with a screwdriver. Replace a screw on each hinge with a carriage bolt. Hinges are on a shed's windows and doors.

I have six hinges on my two shed doors. Each is held on with screws. A bad guy needs ten minutes with a screwdriver and both doors fall off. I replaced one screw in each hinge with a tamper resistant fastener. I chose carriage bolts because they are found in every hardware store.

what it is

I replaced screws with M4 carriage bolts and locking nuts.

The "M4" abbreviation is defined by ISO (International Organization for Standardization). ISO have several standards documents describing threads such as ISO 68-1: "ISO general purpose screw threads - Basic profile - Part 1: Metric screw threads". I can't even read to the end of this title, let alone read the documents.

A carriage bolt has a smooth domed head. The shaft next to the head has a square section. This fits in a square hole and stops the carriage bolt spinning round when you tighten up a nut. Carriage bolts are also known as coach bolts although I believe a coach bolt is a screw with a hexagonal head.

I used locking nuts to hold the carriage bolts in place. A locking nut is a nut with a plastic insert. The plastic insert stops the nut loosening with vibration. A locking nut is commonly called a nyloc nut (nyloc is a trade name made from the words nylon and lock). You need more force- that's "prevailing torque" to you engineers- to turn a locking nut compared with a normal nut.

spend money

  1. Count the number of hinges.
  2. Measure the thickness of the door.
  3. Go to the hardware store.
  4. Buy stuff.
    1. one carriage bolt for each hinge (£5). I bought ten M4 bolts. Six are 100mm long for the door hinges and four are 50mm long for the windows.
    2. a big fat washer to go on each bolt. Buy a few more so you can drop one down an inaccessible gap (£1).
    3. a lock nut for each carriage bolt. Buy a few more to allow for mysterious disappearance. You use these to secure the bolts (£2).
    4. a couple of normal nuts. You use these when cutting the ends of bolts (£0.20).
    5. a roll of paper tape (£2).
    6. a cross-cut flat smooth hand file (£7) for cleaning up cut bolts.
    7. a small round riffler file (£3) to make a square hole.
    8. a screwdriver (£3) for removing screws.
    9. a drill (£30).
    10. a selection of HSS (High Speed Steel) drill bits (£10). I used a 4.5mm drill bit.
    11. a hacksaw and blades (£10) for cutting bolts.
    12. oil (£3).
    13. a spanner (£5). A spanner is like a wrench, only better. This tightens the lock nuts. I actually own a 1/4" square drive, chrome vanadium steel, metric hex socket set (£20) so I used a 7mm socket and ratchet handle.
    14. a vice (£30) for holding bolts while you cut them.
  5. Go home.

cut a bolt to size

  1. Measure the thickness of the door.
  2. Work out how much to cut off the end of a carriage bolt. The bolt end needs to stick out from the hole about 10mm.
  3. Find the roll of paper tape.
  4. Mark the place to cut the bolt by sticking a piece of tape onto it.
  5. Put a normal nut onto a carriage bolt and spin it past the piece that will be cut off.
  6. Clamp the carriage bolt end in a vice.
  7. Cut the bolt end off with a hacksaw
  8. Take the bolt out of the vice.
  9. Find the cross-cut flat smooth hand file.
  10. File down the rough end with the file. This bends the end of the screw thread.
  11. Unscrew the nut. This straightens out the screw thread.

replace a screw with a bolt

  1. Find a screw in the middle of the hinge.
    LIC topography: make a hole for a carriage bolt
    remove a screw drill a hole make it square
  2. Choose a screwdriver to fit the screw head. This is usually a pozidriv.
  3. Remove the screw.
  4. Find a drill bit that is the same width as your carriage bolt shaft.
  5. Drill all the way through the hinge and the door and out the other side.
  6. Find the small round riffler file.
  7. File the hole to make it square. This square hole will stop the carriage bolt spinning round.
  8. Push the carriage bolt into the hole. Push it all the way in so the square shaft is in your square hole, the head end is flush and the thread end sticks out inside the shed.
    LIC topography: fix the carriage bolt
    insert from outside tighten inside done
  9. Put a drop of oil on the thread end.
  10. Put a washer and locking nut on the end.
  11. Find your spanner.
  12. Tighten up the nut.

That's it. Well done. Just 9 more bolts to go.