I have a blue machine from the 50's, it was my mom's who bought it soon after their marriage. On the face plate it has Deluxe Round bobbin Model 385B Made in Japan It's serial is H 7613001. But under the base plate there is a label that said if any questions use model #, serial number and use Sewing Head Model No URR-385B Serial 55X.
URR and UHT may be the head style mine is very 50's modern.