Normally +060 is the last oversize on A10's but I have used some +080's supplied by SRM and they worked fine. STD is the standard manufactured original size which for A10's is 70mm diameter then each oversize is in increments of .020". It was possible to get +030's back in the day but I don't think they are available now. If your barrels are already on +060 and are worn out or scored you will probably need new liners and a set of STD pistons. Take the whole lot to a reputable, experienced engineering firm and leave the rest to them. However, they need to take a bit more material out of the bottom of the barrel than the top or, when fitting the new liners, there is a good chance that the original barrel skirt will split or crack. I would also recommend no less than .004" piston clearance which, assuming good quality pistons, should be sufficient to safeguard against potential seizure when running in (carefully!). Seizing new liners can be a real disaster, to be avoided at all costs!