In a DIY forum the head size is usually important. If your replacing the screw or bolt the rest of the info is at least as important.

Just to be technically accurate whether you call something a bolt or a screw is dependant on how it is used.
"If a product is designed so that its primary ourpose is assembly into a tapped hole, it is a screw. Thus the screw is tightened by exerting torque on the head. If a product is designed so that it is intended to be used with a nut, it is a bolt. A bolt is tightened by exerting torque on the nut" Mechanical Engineering Design by Joseph E. Shigley

That said even in the Mechanical Engineering world fasteners are usually refered to as screws when they are small and have a slotted or philips head. Bolts are larger sized fasteners with hex heads even when they are used as a screw in the definition above.

Paul
1984 300SD
1992 400E