1. Submitted by George Lauderbaugh. Gauge 0 track standard 9mm height.  The "outside" holes and the tie clamp design suggest this should be American Flyer. (The tie-pin arrangement is 3-0, whereas American Flyer is 2-1, but the pins appear of different designs, so that is not helpful one way or the other.) On the other hand there is no camber and no characteristic "step" in the tie. And why would a manufacturer punch four holes in its ties? It is possible that any or all holes were punched "at home", but if so, it was an expert job. It looks if this ought to be American Flyer, but is it?

3. Submitted by "Dave": This is one jim-dandy of a mystery. It is a gauge 0 turnout of what appears to be a venerable vintage. Yet there are holes around the centre rail clamps - a manufacturing practice abandoned very early (by 1920) in toy train track production (except for the Spanish Paya trains).
On the other hand this is a large radius turnout, perhaps 36" or even 48" radius, which as far as we know, did not come to the toy train market until the 1930s.
Another unusual feature is a throw-lever parallel rather than at 90 degrees to the track, contrary to the usual throw-lever or bar designs of the toy train era.
On the other hand, the throw itself is more of a European ground-throw design such as that of Hornby. The track pin arrangement is 3-0, that is to say the three pins at one end, which might suggest Lionel, as the other major manufacturers preferred the 2-1 system. But how to reconcile the primitive centre clamp tie cut-outs with the later-era large radius? And the rather different throw-lever design?

4. This decal (left) appears on the underneath of a pair of Gauge 0 tinplate bridge ramps, presumably manufactured sometime pre-WWII (right). The decal could of course be that of a private owner, but the ramps are a mystery too.

6. Submitted by James Pekarek. This Gauge 0 level/grade crossing was bought as a single item. It no longer had the barrier posts or barriers. Between the rails however there is a platform that would be depressed by the passing wheel flanges, and its evident purpose is to activate the crossing barriers. The crossing's manufacture is of flimsy metal, but the paint job appears original. No identifying marks, of course.