This exact spindle style can be a little nebulous to speak and write about, because it's very common within BMX and a lot of cranks are compatible with it, but to my awareness it doesn't have one agreed-upon name. I think it's just one manufacturer that makes the cranks and spindles for it and it gets sold under about a million different brands, but I don't know the name of that company.
The standard is usually called 8-spline when it's called anything. There are two very common spindle diameters within BMX, 19mm and 22mm, and 8-spline is mostly associated with 19mm; I'm not sure if 22mm versions exist but they might. You should flip your tape measure around and measure the diameter to confirm yours is 19mm.
The way you're measuring implies you're concerned about the spline length, but on this standard the spline length doesn't count for much. This is not a press fit standard and the cranks can land anywhere along the splines. The crank locks into the splines using a pinch bolt. The bolts that go into the ends of this spindle style are for bearing preload only, and also provide a secondary form of security if something went wrong with the pinch bolt. Spindle spacers can be used freely with this spindle type to dial in the chainline, symmetry, and spline engagement. You want the end of each crank overhanging the end of the spindle by 0-2mm. Getting that part right is important and it's up to the person setting up the bike to make extra sure of it, because it won't just happen automatically when you put it all together.
This standard is the ubiquitous one for basic to medium quality BMX tubular chromoly 3-piece cranks, and many companies sell cranks that go on it. If it looks remotely the same and it's a cheap 19mm 3-piece, it's a match, again with the qualifier that sometimes in practice you need some 19mm BMX crank spacers to tune things in. (Part of the reason for this is that the rest of the bottom bracket hardware you have, i.e. the bearing shields, sprocket, and sprocket adapter as applicable, are less standard in thickness.)