Is it the specific form factor that you are after? I don't really see the meaningful difference between a 4.5 and a 5. Other than the .5. They're in the same 'class'. Just curious what mandates a 5 but not a 4.5
I went through this question when I bought my tank and from what I remember there were 2 main brands.
Manchester and
Worthington. There wasn't much difference between the 2 cost wise but shape and dimensions were slightly different. There may be others available and this is mainly concerning vertical DOT steel tanks, not marine or aluminum or horizontal tanks.
Basically what it boils down to is...
-Mancester tanks are labeled as 5# or 10# or 11# tanks
Manchester 5# tank (1.2 gal, 12" tall, 8" dia)
Manchester 10# tank (2.4 gal, 17.4" tall, 8.9" dia)
Manchester 11# tank (just a short squatty 20#) (2.6 gal, 12.4" tall, 12.2" dia)
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-Worthington tanks are labeled as 4.25# or 11# tanks
Worthington 4.25# (note it's base is different) (1 gal, 11.8" tall, 9.1" dia)
Worthington 11# (2.6 gal, 16.8" tall, 9.1" dia)
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And here's the standard run of the mill 20# bbq tank that can be exchanged at many common convenience or hardware stores. These fit perfectly in a milk crate to keep them more stable. Typically ~18" tall and 12.2" dia.
Since liquid propane weighs 4.2# per gallon at 60* the slight differences in tank sizes/volumes are what I believe are throwing off the ID of these tanks and make this somewhat confusing. Anyway, hope this helps clear up some things...