Scarf joint in fir
A scarf joint in fir joins two lengths by overlapping their prepared ends. The overlap transfers the connection along the length of the beam.
Fir proportion
Tredgold (1871) gives about twelve times the thickness of the beam as the whole length of the scarf in fir when no bolts are used. A beam is a long structural member, and the scarf is the prepared overlap between its lengths.