螺丝钉

screw

spiral shell / snail / conch

screw

silk / thread / trace / (cuisine) shreds or julienne strips / CL:條|条[tiao2] / classifier: a thread (of cloud, smoke etc), a bit, an iota, a hint (of sth) etc

nail / to follow closely / to keep at sb (to do sth) / variant of 盯[ding1]

to join things together by fixing them in place at one or more points / to nail / to pin / to staple / to sew on

a "screw that never rusts" — sb who selflessly and wholeheartedly serves the Communist Party, like Lei Feng 雷鋒|雷锋[Lei2 Feng1], to whom the metaphor is attributed