![[Joes]](../marque_file/joes.gif)
Cheese Head and Fillister are head shape types. Cross and Pozi are screw driver types.
Cheese head:
The Cheese Head type is shaped like a disc with cylindrical outer edge. The height is approximately half the head diameter. The screw above is a Cheese Head slotted screw
Fillister head:
The Fillister Head type has a Cylindrical shape, but with a slightly convex top surface. Notice the domed head. The height to diameter ratio is larger than half the head diameter. The screw above is a fillister Head slotted screw.
Cross:
A double-slot or Cross screw drive has two slots, oriented perpendicular to each other, in the fastener head; a slotted screwdriver is still used to drive just one of the slots. The slots do not imitate a Phillip screw and a Philip screw drive cannot be used. The screw usually has a large flattened pan head. The sole advantage is that they provide some measure of redundancy: should one slot be deformed in service, the second may still be used. These screws can be found on some Norton primary and other covers.
Pozi or Pozidriv:
Screws with the Pozidriv head are found on all Triumph and BSA models engine/gear covers and several other areas.
The Pozidriv is an improved version of the Phillips screw drive. Pozidriv was jointly patented by the Phillips Screw Company and American Screw Company. The name is thought to be a portmanteau of the words "positive" and "drive." Its advantage over Phillips drives is its decreased likelihood to slip out of the grove, which allows greater torque to be applied. It is very similar to, and essentially compatible with, the Supadriv screw drive.
Pozidriv drive bits are often designated by the letters "PZ" plus a size code of 0, 1, 2, 3, 4 or 5 (by order of increasing size); the numerical bit size codes do not necessarily correspond to nominal screw size numbers.
Attempting to use a Phillips screwdriver bit is likely to cause damage because the design difference between them is fairly significant even though at first glance they appear to be very similar. A Phillips driver has an angle on the flanks, a pointed tip and rounded corners.
The Pozidriv screwdrivers have straight sided flanks, a blunt tip and additional smaller ribs at 45° to the main slots. The Pozidriv was designed specifically to allow much greater torque to be applied because of its more positive engagement.
The Pozidriv screws are visually distinguishable from Phillips by a set of radial indentations (or "tick marks") set at 45° from the main cross recess on the head of the screw.[7] The manufacturing process for Pozidriv screwdriver bits is slightly more complex. The Phillips driver has four simple slots cut into it, whereas in the Pozidriv each slot is the result of two machining processes at right angles. The result of this is that the arms of the cross are parallel-sided with the Pozidriv, and tapered with the Phillips.
The chief disadvantage of Pozidriv screws is that they are visually quite similar to Phillips; thus many people are unaware of the difference and/or do not own the correct drivers for them, and often use an incorrect screwdriver. This results in difficulty with removing the screw and damage to the recess and/or driver, often rendering any subsequent use of a correct screwdriver unsatisfactory. Phillips screwdrivers will loosely fit in and turn Pozidriv screws, but will slip out of the groove if enough torque is applied, potentially damaging the screw head and or driver. Because the drive wings on a Pozidriv screwdriver are square edged, their fit in a Phillips screw head is even worse, so they are more likely to slip or tear out the screw head.
The screw above is a fillister pozi screw.