sentences:  Less often, the standoff has a female thread in both ends and a second screw is used to attach it to the case.Some standoffs use the M3 female thread (which faces the motherboard) instead of #6-32 UNC, and on a rare occasion a mixture of types can be used in the same case.Version 2.1 of the ATX specification states that the length of standoffs needs to be at least , with their cross sections fitting within square areas centered around each mounting hole on ATX motherboards.