4.50” diameter. Includes the following; bushing 10mm x 1.25 female LH thread (in the trimmer head), bushing 8mm x 1.25 female LH thread, bushing 10mm x 1.00 female LH thread, bushing 10mm x 1.25 female LH thread, stud 8mm x 1.25mm LH, stud 7mm x 10mm LH. Can be refilled with line without dismantling. Average time is 30 secs. Inner wall reduces the amount of dirt that can get inside the head. Lightweight and durable. Large eyelets to enhance line life.