Jack Stud (Trimmer)
A shortened stud that supports the end of a header in a framed wall opening. Also called a trimmer stud. It transfers the header load to the bottom plate and foundation.
In Detail
Jack studs are cut to the height of the bottom of the header and nailed to full-length king studs. The number of jack studs required depends on the header span and load: typically one per side for openings up to 4 feet, two per side for 4–8 feet. Jack studs must be continuous from bottom plate to header — never spliced.