Transmissions also tend to have magnets stuck to the inside of the transmission pan. I usually remove them and use a magnetic ATF drain plug for inspection during any drain/refill. Definitely not a gimmick especially when the transmission is just an overrated rock-catcher.
I do recommend the Magnefine, or any PH8a-sized remote ATF oil filter. If using a remote oil filter, you could stick a filtermag, or equivalent on it. Recycled hard drive magnets work great on screw-on oil filters.
If you must magnetic drain plug it, buy a new plug at the dealer and check the metric size at the local hardware/autopart stores. Also, get the fancy drain plug washer from the dealer.