Male Bspp X F. Metric Swivel

This fitting is designed for hydraulic systems, so you'll want to tighten it enough to ensure a leak-free seal. The BSPP side uses a 19mm wrench, and the metric side uses a 17mm wrench, which should give you enough leverage to get it snug. Don't overtighten, though, or you could damage the threads or the fitting itself.

For tying those two thread standards together, it matches a G 1/4 - 19 male BSPP on one side and an M12 x 1.5 female DIN tube metric swivel on the other, in a straight steel body.

That's exactly what it's built for. One end is a G 1/4-19 male BSPP thread, the other is an M12 x 1.5 female DIN tube metric swivel. The swivel end lets you rotate the metric side during installation, which helps a lot when you're trying to avoid putting a twist in your line. Body length is 35.6mm, so it fits into tighter assemblies without a lot of extra stick-out.