In the US, you can get one hundred 4" mascara brushes for around $5. Eye Tees (cottton swabs with a firm point on one end and a flat tip on the other) cost roughly the same. You'll find them at most beauty supply stores or online. These get into tight spaces. Dipped in mineral spirits (or whichever solvent you've come to like), the brush gets the stuff loose and the Tee wipes it away. Blasting air helps as well. Works for me. Others will have other ideas.
via u/scmowner
https://www.reddit.com/r/typewriters/comments/1jyr2hc/the_best_way_to_get_rid_of_all_this_gunk/
Colloquial advice to use 4" mascara brushes as a replacement for a segment pick for cleaning out typewriters.