Time in “the hole” (also called SHU or segregation) depends on the disciplinary charge and the hearing outcome. There is no fixed length.
Typical ranges:
The decision is made by a disciplinary hearing officer, and behavior while in segregation can also affect how long the stay lasts.
Can they still write letters?
Yes. Inmates in the hole can still:
There may be some limits:
But communication by mail is generally still allowed and is often one of the only ways they can stay connected while in segregation.