Download the R1271NS12x datasheet PDF.
This datasheet also covers the R1271NS10x variant, as both devices belong to the same (r1271ns10x / r1271ns12x) distributed gate thyristor family and are provided as variant models within a single manufacturer datasheet.
Note: The manufacturer provides a single datasheet file (R1271NS10x_WestcodeSemiconductors.pdf) that lists specifications for multiple related part numbers.