sash roller; door roller; sliding door roller
A small wheel or roller attached to the bottom of a sliding door, window sash, or screen to allow smooth movement along a track.
The old sash rollers wore out, making the sliding screen door hard to open and close.
I bought a door roller at the hardware store and replaced it myself.
Compound of 戸 (と, 'door') and 車 (くるま, 'wheel'), literally 'door wheel'. The reading とぐるま reflects rendaku voicing of くるま.