These bobbins should fit the cores of type UY1658 found here:
http://www.aliexpress.com/item/large-watt-U-shape-transformer-ferrite-core-UY1660-machines-equipments-10pairs-lot/493680068.html
This bobbin is based off a similar AR bobbin.
Recommend ABS or PETG or similarly string material. PLA is more prone to break due to stress on the ends of the bobbin.