transformer question again

Hi Guys

i have been looking to source a transformer which will convert 240Vac to 12Vac. However the 12V side must have a current rating of 5amps. Basically what iam going to do it reverse the transformer around so that it becomes a step up instead of a step down. (is it easier this way?) I am using it in an inverter circuit and i hope to have around 60Watts (60 / 12 = 5 Amps)

My question is:

looking on rs components web site they show specs of transformers with 2 * 6V or 2* 12V etc on the output side. Why do they do this? If i want my 12V do i go for one with 2* 12V and only use one or do i go for one with 2* 6V? and use both to get my 12V?

any help is greatful

cheers
andy.

Here is two causes why made the manufacturers two windings:1. the PCB transformers for low profile the primary and secondary 2-2 independent windings, 2*120 and 2*12 etc. 2.With two secondary need only two diodes for full-wawe rectification.
If You need really only one 12V, choose the 2*6V type and connect the secondaryes serial.
For an inverter (from 12VDC to 220VAC) also better the two secondary type, in this case need only two power transistors, but i recommend the 2*9V secondary.