The reason for the brass spool covers is the original Remington design. In the diagram from the Operating Manual below you can see that spool covers, numbers 6 and 26, are elegant. I want to make covers that are similar, but in brass.
Each spool has a 1/4" post in the middle that the knob of the spool cover fits.
There's a good picture of what theNoiseless 7 looks like at this link: http://site.xavier.edu/polt/typewriters/remingtonnoiseless7.jpg
I think you would agree the original spool covers look good.
I'm guessing that the 1/2" by 1/2" small brass knobs from Lee Valley will fit if I drill them to 1/4", but it could be that they are smaller in diameter at the waist. In that case I have a backup plan. With 9/32nd brass tubing ( internal diameter 1/4" ), and washers drilled out to fit the tube, I can make up knobs to fit from scratch.