Insurance company question

I know coverage works differently for each insurance company but I also believe they have their standards pretty much the same thru out the industry. So, my question is what is the normal for insurance company coverage on mask, cpap machine and say parts filters etc for insurance companies?

I understand mine will replace filters at 3 month intervals and I think the mask in 6 months but what are the norms for this?
thanks

Check here:

http://www.puritanbennett.com/remb/sleep.aspx#coverage