TGP Helidon (Tovarna gramofonskih plošč Helidon) was a Yugoslav record plant located in Slovenia and associated with the RTV Ljubljana and was active in the custom/private pressing business as well.
Helidon pressing numbers most commonly appear in the runouts of a record only, not on the labels. They include:
UFLP ### - custom LP (generic number)
USP ### - custom 7" single (generic number)
UEP ### - custom 7" EP (generic number)
USSP ### - 7" single pressed for Suzy
USLP ### - LP pressed for Suzy
URSP ### - 7" single pressed for RTV Ljubljana
URLP ### - LP pressed for RTV Ljubljana