上部構造
assembly
bed
bolt
broken
close
connection
construction
corrosion
crushed
decay
design
fastening
female
fitting
hex
hexagon
hexagonal
industrial
industry
inside
internal
iron
joint
line
nut
pin
rail
railroad
railway
road
rock
screw
screwed
sleeper
steel
stones
stud
substructure
system
technique
thread
threaded
tie
timber
track
traffic
transportation
union