seam gauge (thing)

Sewing - a measurement tool, particularly for setting and checking seam allowances.

Seam gauges come in one of two forms:

1. A small metal ruler with a slit down the center. In the slit is a sliding plastic piece. The whole assembly acts like a set of calipers.

    _________
    \   __   |
     |- | |  |    <- ruler
     |- |_|  |_
    /|- | |  | |  <- plastic slider
    -|- |-|  |-
     |- | |  |
   

2. A cross-shaped metal plate, each of whose arms is a standard length. The lengths correspond to the commonest seam allowances.