Last weekend, I tried to install a Fumoto oil drain plug. It should just screw in, but it kept binding. I'd get it to go about 3/4 turn, and it would bind like it was cross-threaded. I fiddled with the thing for 20 minutes, then gave up and used the stock drain plug - which screwed right in with no fuss. I have the F-105 (listed in the size chart at "20mm-1.5"). I can't find spec's on the stock drain plug, but this is what they sent when I told them I have a 2002 WRX. I feel dumb asking for suggestions (er, did you turn it clockwise?), but I can thread a bolt, so I feel dumb just giving up, too. DD
they tend to leak sometimes, I'd say sell it and be done. Did an oil change today, it wasn't too big of a hassle to remove the drain plug and throw a new washer on it. Did you check thread and pitch visually? If not give the vendor you purcahsed from a call or email.
I love my drain plug and would say it was worth every penny. However, mine screwed right in, no problems. I would check and see if there are any irregularities in the drain plugs threads, and if it still doesn't work, return it and get a new one. No matter how tight tolerances are at the Fumoto factory, you might have the one in a million that got through. f-105 is the only model they make for all Subarus AFAIK.
Mine screwed right it but did leak for a while when I installed it. Not a bad leak but a very slow drip. I didn't want to turn it any tighter.. I drove it around the block and wiped it down and waited, and it didn't leak again. I checked under the car daily and check oil levels and it seems to be fine... pretty scary for a second there.....