Is this a Parker 21 or a 51?

[jbb]

[jar]

"21"

[jbb]

Thanks. Which parts of the pen tell you that?

[Farmboy]

Super 21. The metal jewel is the first clue. The tubular nib makes it a Super 21.

[plistumi]

What's a tubular nib?

[nxn96]

I'm guessing this is a Super 21, based on the cap. The filling system with the "hoop" over the sac is a 21 design, but keep in mind that the Parker 51 Special used the same design. The usual "clue" is what is imprinted on the lower part of the filler: A 51/51 Special or 21 usually had the model number on the metal part of the filler unit. I can't say for all the Super 21's, but those I've run across typically have simply "Parker", with not model number. If this pen has "Parker", with no model number, I'd guess Super 21.

Hope this helps.