tail classified in a subclass lower in the schedule, both in the same
class, if the subclasses are so related that the combination always
involves the detail so that a search for the detail must necessarily be
made in the combination subclass, the patent may be placed in the
combination subclass. This avoids the need of a cross reference into the
combination subclass, and a lack of a copy in the detail subclass is
immaterial, as it is seen in the completion of the search through the
combination subclass. (See Rule 19.)

Example: A patent for a saw-making machine discloses
dressing, jointing, and gaging mechanisms; it claims
dressing and jointing only. There is a subclass for
dressing, jointing, and gaging, and a subclass for dressing
and jointing. In this case the patent may be placed in the
first-mentioned subclass, as that must be searched always
when the second-mentioned one is searched, cross
referencing in this situation being of little value.

(22) Where a subclass with a generic title has indented thereunder a
species type-subclass bearing the title of the generic subclass
qualified by a difference, any patent which claims an invention falling
within the genus subclass and discloses the qualification of the species
type-subclass should be classified in the latter whether or not the
entire disclosure is claimed. (See Rule 19.)

Example:

Class 29.--METAL WORKING.
Machine chucks and tool sockets--
Cam closing--
126. Scroll--
127. Bevel pinion or ring.

If a patent claimed only the scroll of a scroll-chuck, but
disclosed it in connection with a bevel pinion and ring, it
should be classified in subclass 127, Bevel pinion and
ring, and not in subclass 126, Scroll, although if there
were no disclosure of the bevel pinion and ring it would go
in subclass 126. Any search for scrolls must be prosecuted
through all subclasses that include "Scroll" in the title.

(23) Where, as in the case of patents that show and claim a combination
that as matter of common knowledge is not new except in one of its
elements, to classify a patent strictly in accordance with rule would
result in placing the patent where it would serve no useful purpose as a
reference and having to cross-reference it to a class where it would
serve a useful purpose, it is best to classify the patent in the class
to which the element would take it. (See Rule 19.)