** 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. 

I designed these for my own typewriter as shown, and this is an experiment to see if it's worth my time to make some more for the community. If you have access to a 3D printer, I have shared this design online here, feel free to print your own: https://www.thingiverse.com/thing:4813986

Ok, so this auction is for two sets of 2 spool nuts printed in Midnight Black NinjaFlex TPU FLEX polymer (so, 4 nuts total). You only need two for a machine, but they are small and get lost easily, so you get four in this auction. Or, fix two machines!

Some of the photos show my typewriter, or the original metal spool nuts for comparison, they are not included. You will get 4 black NinjaFlex nuts.

These can also be printed in rigid plastics in many colors (but without the retention feature), and other NinjaFlex colors too. If you are interested in a different material or color, send me a message and I will see if that can be done.

** Does your machine need spool nuts? **

As far as I can tell, the Corona 3 machines starting in about 1922 have a new design including a different ribbon system. According to a later version manual "The new Corona (serial numbers above 500,000 is equipped with an automatic ribbon reverse which makes it unnecessary for the operator to pay any attention to the ribbon save to replace it when it has been in use so long that its ink is exhausted. Both ribbon and spool used with the Automatic Reverse are slightly different from those used on earlier machines and are therefore not interchangeable." You can download that manual here: https://site.xavier.edu/polt/typewriters/Corona3-1920.pdf. I have only used the original Corona 3 (mine), so I can only point out what I see online, later pictures on TWDB don't seem to have spool nuts, and this manual does not describe them. I have uploaded two new photos of my machine showing what yours should look like to use these spool nuts.