The most common form consists of a handle, shaft and head. The head is usually forked with a cutting surface situated at the base of the fork. In some designs, one side of the fork tapers to a sharp point to allow easier insertion in tight stitching.
In use a seam ripper, the sharp point of the tool is inserted into the seam underneath the thread to be cut. The thread is allowed to slip down into the fork and the tool is then lifted upwards, allowing the blade to rip through the thread. Once the seam has been undone in this way the loose ends can be removed and the seam resewn.