I would like to bolt a bracket to a steel pipe (1.5 inch diameter), with the nut located inside the pipe. Since the application needs to support a considerable amount of weight, I need some kind of washer or spacer that is flat on one side but spherical (or cylindrical) on the other side, to match the inside surface of the pipe. I'm afraid that a regular washer will buckle and/or crack under the pressure, since the force would not be distributed evenly. What can I use to solve this problem?
Washer / spacer for round surface
boltsfastener
Related Solutions
You probably don't want to do that anyway! Think carefully of what your request would mean.
A 3/8-16 thread means that the width of the bolt is essentially 3/8 inch, but what matters here is the 16. That tells us the thread pitch is 16 threads per inch. The nut being about 3/16 inches thick means that the bolt and the nut mate on three threads. A thinner nut would have less thread contact, so less strength.
If you really need a thinner nut, then it will be easiest to use a smaller diameter bolt. They have finer threads, so the nuts are also correspondingly thinner. Of course, I don't know why it is that you have chosen a 3/8-16 bolt. You may also choose a different thread pitch for your bolt. The 3/8-16 thread pitch is the standard (coarse) thread that you will find in nearly all home stores. However a more diligent search will find bolts and nuts with a 3/8-24 or even a 3/8-32 thread. They may have nuts in a different thickness.
Perhaps more important than the size of the screws (or other fasteners) is what they actually grasp. With any significant load, a screw will not hold by itself in tile or plaster. The tile will chip and the plaster will crumble.
One possibility is to use an anchor through the tile and plaster that expands laterally. There are several types (plastic, metal, etc.), but these are also generally used for lighter loads that are close to the wall, not a shelf that sits on brackets that act like levers, tending to pull them through the wall:
If your plaster is attached directly to masonry, there is an expanding anchor that is meant for that:
It must be placed in the masonry, not the plaster.
If there is a hollow space behind the plaster, a third type of anchor that mushrooms behind the surface could be used:
A fourth kind is a toggle that is inserted folded, but then opens behind the surface of the plaster and its fastening:
If the wall behind the plaster is hollow, this may be the best type of fastener.
If there are studs behind the plaster, the strongest fastening is to align the brackets with the studs and go through both the backsplash, plaster and finally into the studs with wood screws (wooden studs) or screws designed for metal studs.
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Best Answer
Most washers will flex somewhat, so unless it's a really small pipe, or you're installing in really cold temperatures, you shouldn't worry ... but I'd be more concerned with being able to hold the nut still while you're trying to bolt to it in a smaller diameter pipe. (I don't know if the 1.5" is ID or OD, but if it's outer diameter, and it's got any significant wall thickness, it's going to be tight)
If you're really concerned, you should be able to find a rubber gasket to put in there to take up some of the gap; you could also cut down a rubber grommet or bushing to fit in there. You could also use multiple thinner washers which will flex more easily than a single thick one.
Another option would be to take a hole saw that's got a similar inner diameter to the pipe, cut a plug of wood, then slice a chunk off to make the flat-on-one-side-curved-on-the-other piece you're looking for. (and then use a fender washer or similar so the nut doesn't dig into the wood).