This is a single shoulder strap for Pionier-Battalion Fürst Radziwill (Ostreußisches) Nr 1. The oldest of all Prussian Pionier Battalions, it was raised in 1780. It was garrisoned in Königsberg I. Pr. and assigned to the I Armeekorps. The red shoulder strap features its unit number embroidered in yellow on the obverse.
The strap measures 2 ½” x 5 ¾.” It may have been for a great coat, as it is considerably larger than the type used on a tunic. Some soiling appears on the obverse, while substantial mothing marks the dark-blue backing.