Browsing in Hull's sole remaining record store* this morning I came across a CD entitled "Gob Iron" (or perhaps "Gob-Iron, memory fails). It was a collection of blues harmonica recordings. I was surprised, I thought that this expression was peculiar to Hull. Clearly not. I like 'tin sandwich' but preferred what I thought was local slang. I must do some checking.
*No name, no publicity. It's one of those chain outfits that change their name every so often, but never get any better. I don't like patronising it, but the other options are second-hand 'specialist' shops that overcharge.