Once you have one you'll wonder why it took you so long to get one. It is so convenient to reach and write immediately. No fussing with a cap. Especially if you like to post your cap on the barrel. And where did that cap or pen go on your messy desk anyway? Nope, the deskie is right there where it always is. Old reliable is ready at hand.
This pen is from as early as 1930 based on evidence I can find in old Sheaffer catalog scans.
"J74D, Lifetime desk fountain pen. Code ZYUBO. Jade green, unbreakable Radite, medium diameter, with gold filled fittings."
Most catalogs I have list desk pens in only small diameter and medium diameter. It seems there were no large diameter (OS) desk pens. I could be wrong.
Jade Sheaffer celluloid (Radite) does not often age gracefully. Many of them have long since turned brown and murky looking. It is evidently due to a combination of UV exposure and deterioration from off-gassing of latex rubber ink sacs. Fortunately this pen has only a hint of discoloration at the joint between the barrel and grip section. It's in almost rare condition. I've replaced the sac with silicone so there will be no risk of latex contamination in the future. And you can use whatever ink you desire without fear of melting a latex sac.
The only other notable imperfection on the pen is the black ebonite extension has a few flea bites and is blunted off perhaps 1/4" (~6 mm) shorter than original. The desk base has very small chips from 3 corners. The socket is in perfect condition.
The nib is firm with a smooth, wet fine point that writes with a bit of nice character and variation due to its subtle tipping shape.