The staff bead is the moulding fixed around the inside face of a box sash frame, holding the lower sash in its channel. It is the innermost bead — the one you touch from inside the room — and it is fixed, not housed in a groove, which is what makes it removable.
It has two jobs. It keeps the bottom sash running in its channel rather than tipping into the room, and it closes the gap between the sash and the frame against draughts. Because it is only pinned in place, it is the first component removed whenever a sash window is serviced.
Staff bead and parting bead
The two are easy to confuse. The staff bead sash window arrangement runs as follows: the staff bead is on the room side, holding the lower sash; the parting bead sits in a groove machined into the pulley stile, between the two sashes, keeping them clear of one another as they pass. The staff bead is usually a shaped moulding, while the parting bead is a plain rectangular strip. Taking the staff bead off releases the lower sash; taking the parting bead out releases the upper one. Both have to come out to reach the weight pockets and the cords.
Why staff beads fail
They are removed and refitted many times over a window's life, and each time the mitres are stressed and the pin holes enlarge. Eventually the bead no longer sits tight to the sash and the window rattles in the wind. Painting over a loose bead year after year makes it worse: the paint film glues it in position until the next person prises it off, splitting the timber along its length.
Where beads are sound they are carefully eased off, labelled and refitted, since the original timber is denser than modern equivalents and the profile is already correct for the house. Where they are split or over-painted they are replaced with beads run to the same section.
New beads are also the natural place to conceal draught-proofing. A seal set into a routed groove in the bead closes the gap around the sash without anything being fixed to the face of the window, so the improvement is invisible once the paint is on, and nothing about the appearance of the window changes.