Perhaps firearm threads, they are typically very fine thread, even on
American weapons.
Steve

"Novice" wrote in message
. ..
Hi, recently I was given a set of taps and dies of special kind. As there
a
M 1,5 x 0,35
M 2 x 0,45
M2,5 x 0,45
M 3 x 0,6
M 4 x 0,75
M5 x 0,9
Does anyone out there in the metric world know where those strange sizes
are (were) used for??

Novice