The US is changing to metric, and I'd be surprised if the current Chinese B&S engines are not metric (though I've been surprised before - it happens). 7 mm is 0.276", which is a bit less than 9/32" (0.281"). Holes in gaskets are always oversize to allow clearance around the bolts or studs that go through them - your 7 mm hole may be intended to allow clearance for a 1/4" (0.250") bolt.
