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54 Making Things Move

FIGURE 3-2 Screw anatomy

The easiest way to join two materials with a screw is to drill a clearance hole through
both of them, insert a screw that is longer than their combined thickness, and use a
nut on the opposite side to sandwich the pieces together, as illustrated in Figure 3-3.
As a rule of thumb, make sure the screw extends all the way through the nut and
sticks out at least two or three threads past it. The right clearance hole gives you just
enough room to put the screw through, but not so much that it’s sloppy. A close fit is
standard, but a free fit is a little larger and will give you more wiggle room for poorly
aligned parts.

Sometimes it won’t be possible to use a screw and nut due to space or other
constraints. In this case, you join the two parts by screwing directly into one of them.