Abstract: The invention is of a thread indication kit for use in determining the specification diameter and thread density of a threaded in-take orifice of a spin-on filter, such as the traditional oil filter used in motor vehicles. The kit includes a groups of sizing tabs, each of which includes a sizing lobe. The sizing lobe is a blade-like member with parallel and spaced edges separated by a distance which corresponds to the thread crest-to-thread crest distance of diametrically opposed points within an in-take orifice of an oil filter. Displayed on each sizing tab is indicia which indicates the specification diameter of the intake orifice which exhibits the thread crest-to-thread crest distance corresponding to the lobe dimension of the sizing tab. Applicant's kit also includes a thread gauge which is used to determine the thread density of threaded orifices.