I had the same question, this is what I found in the COLLISION INDUSTRY CONFERENCE Glossary of Terms

FISH PLATE: Repairing of a cracked frame rail by first of all welding the cracks and then reinforcing

the rail by welding another plate that covers and extends well beyond the repaired area. per http://www.ciclink.com/terms.htm#gtf


The American Heritage« Dictionary of the English Language: Fourth Edition. 2000.

fishplate

SYLLABICATION: fishÀplate
PRONUNCIATION: fshplt
NOUN: A metal or wooden plate bolted to the sides of two abutting rails or beams, used especially in the laying of railroad track.
ETYMOLOGY: Probably from French fiche, peg (from Old French; see microfiche) + plate.

<img src="/forums/images/graemlins/cheers.gif" alt="" />

ED