on-the-fly
on-the-machine
on-the-spot
on-time
OOP
OOPS
OOR
op
opal
opaque
  open
open-air
open-architecture
open-back
open-center
open-chain
open-circuit
open-cycle
open-end
open-ended
open-face

    open tolerance part

     деталь без требований к точности

     деталь с открытым допуском