Abstract: An improved plastic spool for serving electrical insulation, such as glass fiber yarn, about a continuous wire is provided having a better combination of strength and breakability properties than prior spools. The spool is made by joining two identical molded halves, and comprises a hollow tubular core and radially extending flanges at each end of the core. The flanges are tapered in thickness and are reinforced by integrally molded stiffening ribs. The flanges are provided with grooves along which the plastic will fracture, which grooves are aligned with slots in the core. The slots extending axially along the core but terminate a distance from each flange such that the core is not weakened, yet the fractures along the groove lines will propagate across the remaining solid plastic continuum and connect with the slots to fragment the spool into pieces. The spool also includes a paper insert which lines the core of the spool for snug engagement with a mandrel.