Some SFG2s are ferrous, some aren't! I've got two, one of each. I think one is from the 1970s and one from the late 80s. The non-magnetic one is the later one. If buying new I'd ask the seller to guarantee it was non-ferrous, I'd expect all modern ones to be so as it's obvious they'd be used with MC carts these days. Even so check it with a magnet before using it! I really like it as a tracking gauge, so worth getting a nice one - it's apparently a lot more consistent and accurate than many of the digital ones.