Then bend up each arm so that your crest block fits between them, and finish the tips by curling them down. Anneal the metal before each step. Making sure that the center post is the right height to support the crest where you want it, bend the bottom end to form the foot or tongue, and grind or hammer it flat to fit the holder on your helmet. Finally, file, sand, and polish it well. The arms can be squeezed slightly at the top to give them a firm grip on the crest block.
Many depictions show a comparatively short block mounted directly on the helmet.
Coolus helmet crest knobs often have a slot crossed by a hole. The crest block would be quite short in this case. Montefortino helmets generally have a knob with a vertical hole. While you will probably want to display your crest when not in use, it is better to store it carefully. It is one item of equipment which should not show wear and tear from campaigning.