Spanish bicycles typically used French threading until around the mid-1980s. The lack of brazed-on fittings in conjunction with forged dropouts having an integral hanger, long axle slot and eyelets, suggests 1970s and most likely boom era. As such, the seat tube is probably metric standard, with a 28.0mm outer diameter. As noted by John,the post diameter will be a good indicator of tubing grade. The frame appears at least mid-range, with mostly non-OEM components.