Green’s Dictionary of Slang

(US tramp) a tramp who works as a part-time carpenter.

1927		in ‘Jargon of the Und.’ in DN V.
1930		‘Dean Stiff’ Milk and Honey Route 35: Hobos are known for what they do, or do not do [...] One who works on wooden bridges and trestles is a ‘splinter belly’.
1949		Monteleone Criminal Sl. (rev. edn) 220: splinter belly A rough carpenter.