** Note not all Corona 3 typewriters require these nuts, see below **
*** This auction is for 1 set of 4 spool nuts. If you choose quantity 1, that's what you get. Quantity 2 means 2 sets (8 spool nuts) ***
*** As an FYI, I see others have found metal thumbnuts which apparently have matching thread and will fit the Corona 3, selling them for 2 at about this price. Just know what you are buying, the originals have a metal spring inside, and a regular nut will not latch on--during typing, they will fall off. While this listing isn't metal, they look pretty cool in matching glossy black, and they mimic the spring function and will stay on!
Note, this auction is just for Spool Nuts, and is related to my other auctions below:
Full Kit: https://www.ebay.com/itm/174799840230
Typewriter Feet: https://www.ebay.com/itm/174709052038
Case Inside Feet/Rubber/Pads: https://www.ebay.com/itm/175808971517
Basically, EVERY piece of rubber on these ~100 year old machines needs to be replaced, so I suggest you don't buy just these parts, but instead purchase the above kit which includes everything at a better price. But, people have asked, so I have the individual parts listed as well.
The ribbon spools on some Corona 3 typewriters are somewhat unique, and will not operate without the spool nuts which both retain the spool, and select the direction of ribbon travel. Both spools are actively rotated clockwise during typing (including the spacebar), but because they are fed from the front (left spool) and rear (right spool), this clockwise rotation causes both spools to try to pull on the ribbon. Ribbon reversal is manual, you must loosen the nut on one spool, while the other one must be tight. Both loose, no movement. Both tight, something may break as they both try to wind.
These frequently are lost on these ~100 year old machines. You can't just replace them with a matching nut (if you can find one), as the originals are quite sophisticated, actually, they have a built-in retaining clip mechanism that uses a spring force to keep pressure on the threaded rod, keeping the vibration and rotation from unscrewing the loose nut (the one that is tight will be retained by the friction from retaining the spool).
For fun, I wondered how replacement nuts would look 3D printed, and what material would be best. I tried rigid PLA, PETG, and Nylon, and all worked fine. My silk silver PLA looks quite striking, actually, and closest to the original look. The Nylon felt great and would be of course the most durable. But, how to solve the spring retention problem?
It finally hit me that using FLEX material, and redesigning the thread to be a bit small, would solve the problem! Screwing it on, the material expands to fit the threaded rod, but that generates a retaining force (like the original spring mechanism) that keeps the nut firmly on the rod despite any vibration or rotation at all times, not just when not snug against the spool. I actually think this is superior to the original mechanism. Printed in black NinjaFlex (https://ninjatek.com/ninjaflex/), on a smooth build plate, the top ends up glossy and shiny and looks fantastic. After all, this machine is painted in glossy black (stunning) paint, and there is already plenty of gleaming accent chrome, I think these somewhat glossy black NinjaFlex nuts are a really good look. And they function properly.