The inside diameter is 1/8" . I've looked at 3 oil filters (off of AD Trucks ) all the lines are 1/8 ID and none of them had restrictors (they could have been removed ). Jerry I've looked in every book I've got and can't find Either 1/8" or 1/16" ....I'm going with this set-up unless I can find or be shown where 1/16" is right and 1/8" not ....also I can't find any jobber selling restrictors for oil filters ....
