Noggings, Dwangs, Shims and Fake Spots

There was talk of noggings on Grand Designs last night. It was a repeat, of course, and I was rather more than half-watching it because it was a rare departure from the usual egotist-builds-big-glass-house formula (it was the one in which a group of likeminded and impoverished families self-build wooden houses and create a thriving little community). Anyway, the noggings came in when they were assembling the wooden frames. Kevin McCloud (looking very young) talked airily of putting in some noggings. Noggings – also known as dwangs – are small bits of wood used as bracing pieces between the studs or larger members, giving rigidity to the structure. This rang a faint bell – isn't there something similar in a Kay Ryan poem? Not a nogging, but another kind of small filling-in piece, a wedge or fillet, completing a structure... What was the word?
The word was shim, and the poem was this one, Fake Spots –

Like air
in rock, fake 
spots got here
really far back.
Everything is
part caulk. 
Some apartments
in apartment blocks
are blanks;
some steeples
are shims. Also
in people: parts
are wedges: and, 
to the parts they keep
apart, precious.