Bob and Wheel is the name for a metrical pattern frequently used in alliterative poetry at the end of a stanza. The bob is a short tag followed by a wheel, which is a quatrain of short lines rhyming abab:

On many bonkkes ful brode Bretayn he sette,
Wyth wynne,
Where werre and wrake and wonder
Bi syþeú hatú wont þerinne
And oft boþe blysse and blunder
Ful skete hatú skyfted synne.
(GGK, Vv. 14-19)

In this case the bob is formed by the line wyth wyyne and the following quatrain is the wheel.