Attached to the respective yards of square-rigged ships are smaller spars, which can be extended, thus lengthening the yard, thus receiving an additional sailing wing on each side. These are called studding sails, and are used with fair and light wind only. The wings are named after the sails to which they are fastened, i.e. the main studding sails, main top studding sails, and the main top gallant studding sails, etc.[4]