I need replacement strings for my Mexican fender Stratocaster and have got very comfortable with the old strings so would like to get the same ones. What guage and model of strings do the guitars come with as standard? Thanks
Just like it says on the Fender site: Fender® USA 250L, NPS (.009-.042 Gauges)
typically 9-42 or 10-46 gauge. and probably Fender brand nickel-wound.

I personally used D'addario and Ernie Ball Nickel-wound. if you want strings that last longer then I suggest Cleartone brand
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
The Fender 9s are quite nice, I was D'Addario and EB user for long time but came upon the Fender cheap in a 5 package and am impressed. Don't know if that's what they put in guitars on the shelves, from what I know it is Chinese cheapies, but try a set of Fender strings or D'Addario 9s.
Thanks for your help. This might be a silly question but when the string is wound around the tuning head (on a modern style) why does the string not just slip out. It seems like large tension would cause it too especially when the excess string ends have been cut off at the tuning heads. I know you can do special methods but I'm just referring to normal winding around.
The string is fairly stiff and there's plenty of friction from the metal-on-metal contact, so once it's wrapped around the post once or twice it doesn't take a lot to keep the rest in place. In fact more tension makes it harder for the string to come out, similar to how tightening a knot makes it less likely to slip apart.

Wrap a string around your finger a few times and then pull the end. Feel where the tension is located? It's almost all on the first wrap, so you just need enough friction to keep that last wrap in place and the rest will stay put under tension. You're really pulling on the post, not on the rest of the string. The wrap locks the string to the post pretty effectively under tension.