Coolus 'A'

• Simple hemispherical bowls with a small projecting peak at the back. The lower rim at the front and sides was 'knocked back' to form a thickened lip that did not usually carry on to the edge of the neck guard.
• Some examples have simple lines of punched ornamentation and some have a roped border like the early Montefortino types, though others are plain and unadorned.
• They have a single hole or rivet at the side for attaching the chin strap or tie. Roman 'jockey-cap' helmets always have two, sometimes three, rivets to secure the cheek plates. 
• There is no form of knob or plume attachment. In most cases there is a hole in the centre of the neck guard or just above on the occipital region for a carrying ring or a third attachment point for a chin tie.

Coolus 'B'

• Bowl is rather globular with the rim flanged at the bottom and sides, running into the very small neck guard. 
• There is no provision for a reinforcing peak.

Coolus 'C'

• The skull is bulbous and low in height. 
• The neck guards are small and flat and swelling a little at each side before curling in to join the sides of the bowl.

Coolus 'D'

• Skulls are of moderate height.
• Lower rims are 'knocked back' to a rectangular section.
• Small neck guards have a thickening on the underside edge.
• Applied crest knob can be (a) small, solid conical-headed or (b) slotted to take a crest.
• Reinforcing peaks are of right-angled section. 
• [May be contemporary with Montefortino D.]

Coolus 'E'

• Bowl height varies considerably in this group.
• Reinforcing peak is a flat, curved strip of bronze, riveted at each end to the skull and tongued at the centre where it is passed through a slot in the front of the skull and is then bent over.
• Lower rim, although 'knocked back', seldom shows more than a slight projecting lip, which may continue around the upper edge of the neck guard. 
• Crest knobs are slotted from front to back.

Coolus 'F'

• Similar to the 'Coolus E', but the neck guard is made broader at the sides where it terminates with a short, angular step instead of curving in to join the lower rim.

Coolus 'G'

• Distinguished by the increased size of the neck guard - almost twice the width of previous designs.
• Reinforcing peaks are flat strips of bronze that vary in thickness.

Coolus 'H'

• The skull is a low hemispherical bowl with a broad flat neck guard the projects at right angles to the sides.
• The peak is of right-angled section and tapers in to the point of attachment at each side. 
• The lower rim across the brow is finished with a band of filed moulding (possibly inspired by the applied bronze strip on Imperial Gallic helmets).

Coolus 'I'

• Have a deeper bowl in the occipital area, with very broad neck guards. This results in a 'step-down' at the rear of the helmet.
• There may be a carrying handle on the neck guard.