Would the same also apply to other abbreviations such as km (kay-em) instead of kilometer?
I can see an advantage to reading millimeter as mm (em-em) because it's quicker to say.
Aussies say k-g but it depends if it's ok to use slang in the situation.
Kilograms can be referred to using the terms "kilos" or "kaygee". In Ireland we use kilos instead of kaygee.
Never heard of "kayem" before, but "kays" is used as slang for kilometres.