Reamer and Shoulder Bolts Differences

Remember that when axial force is applied (a bolt of any type is tightened) the shank diameter will decrease by a small amount, proportional to the applied torque. The end result is that a near-fit or even interference fit reamer bolt may not still be an interference fit when it is brought up to full tension.

With that said, 'reamer' bolts, 'stripper' bolts, and 'shoulder' bolts are extremely similar. All are designed to take significant shear force. In stripper and shoulder bolts, that shear force comes from the bolt being used (usually) as an axle or linear shaft, while in a reamer bolt, that shear force comes from torque applied to a coupling.

There are only 2 real practical differences between reamer bolts and shoulder/stripper bolts:

1) Shoulder/stripper bolts typically have a thread diameter a few sizes smaller than the shank diameter, while reamer bolts have a thread size close to or the same as the shank size

2) Shoulder/stripper bolts have a machined flat face at the bottom of the threaded section, so that the bolt can be threaded into a plate and the head will be in a fixed, known position. Reamer bolts usually have a tapered and ground transition between thread and round shank.

The end result of this is that for a given shoulder diameter, a shoulder bolt has a lower axial force (bolt tension) limit than an equivalently sized reamer bolt does. You can use a shoulder bolt most places you can use a reamer bolt- if your design can handle a lower level of tension without joint failure.

There are lots of places that shoulder/stripper bolts get used where you cannot use a reamer bolt- shoulder bolts are often used as guides for things like multi-stage stamping dies, where the bolt is threaded into a base plate and the head is used to contain spring force driving the active side of the die apart from the static side. Shoulder bolts are used for this because they can be threaded in and tightened with the flat face at the base of the thread against the base plate, so many can be installed on the same plate and give a consistent head height without requiring any adjustment.

struclearner,

I am not familiar with reamer bolts. I am just reading up on them here, and it appears to me that parts are assembled, clamped, drilled and then reamed. It sounds like you are reaming for a press fit. The holes line up because you drilled them together. Your joint is reliably loaded in shear. Hopefully, the two clamped parts have the same thermal expansion coefficient.

The proper application of shoulder screws is that you tap holes in one piece, and drill accurate holes in the other. Hopefully, everything lines up. For a screwed assembly with hole clearance C, your positional tolerance must be...


The positional tolerance needed to line up precision holes is not fabricateable. If you have two shoulder screws, you can slot one hole. There is no point adding a third shoulder screw. This is very poor design for structural shear, since in some directions, only one screw is loaded.

Positional tolerances are discussed at length in forum1103.

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JHG