====== 2020-10-23 - screw it... ======

{{ :blog:2020:10:23:lead_and_pitch.png?400|https://upload.wikimedia.org/wikipedia/commons/0/00/Lead_and_pitch.png}}

i'm working on a pet project. it actually already spinned off a couple more child projects. one of them i hope to cover shortly. as a part of this effort a needed to screw down one part. thread was [[wp>metric screw|M10]]. i'm always using metric screws, in couple different sizes (depending on length / strength / weight parameters): M2, M3, M5, sometimes M8... and do so for many years now. this time i needed M10, which is much bigger than i typically use, but still -- the same standard. so i made a trip to the shop just to buy two nuts and washers -- around 0.2EUR total. when i got home, it turned out that the nut does not match thread!

i suspected that it was not M10 but instead some imperial-rooted thread, that some1 accidentally rated as M10. but no -- i checked multiple sources and all of them reported it as M10. so i did some reading and when i was finally able to "ask the right question" in the growser, it turned out that for standard metric system screws, you can have [[ISO_metric_screw_thread#Preferred_sizes|different thread pitches]]: coarse ("default" one, if not mentioned otherwise) and fine (that in turn can also come in a couple flavors).

the notion i was used to was eg. M10x50, which reads: M10 screw (i.e. 10mm diameter), 50mm long. this is the coarse pitch -- default one. for M10 it is 1.5mm pitch, thus the full marking would be M10-1.5x50. for "fine" threads of M10 you can choose among M10-1.25 and M10-1.

> "the good news about standards is that there are so many of them to choose from"
[[wp>Andrew Tannenbaum]]

now i need to go back to the shop and look for more M10s, but with a (new measured), non-default pitch: M10-1.