I have a couple of Parker pencils with jewels, so I'm sure they're 51 pencils, and a couple of pencils with clips and tops that look like a 21, so I'm sure they're 21 pencils. I also have a couple of pencils that have arrow clips and resemble the 51 pencils, but they're smaller and don't have a jewel on top. Instead, the very top looks more like the 21 (metal, slightly conical). One also has a shorter clip than the other, so maybe a date or size difference? Does anyone care to guess what models they might be without a picture?

I'll try to get a clear picture or two tomorrow.

Gonna need a picture to answer this, the more detail the better