It is not uncommon for examiners to dismiss dimensional claim limitations—especially relative dimensions—as mere design choices that don’t patentably distinguish over the prior art. Examiners often cite MPEP § 2144.04(IV)(a), which explains that a change in proportions of a prior art device is obvious unless there is some new function achieved. It’s an easy move for examiners to use this in rejecting claims if the “only” difference between the claimed structure and the prior art is that some relative sizing is missing. Examiners will typically characterize this difference as an obvious design choice and summarily assert that no change in function occurs.

But as practitioners know, relative dimensions or sizing can often be an important distinguishing factor of an invention. Changing proportions can fundamentally alter how a device operates, even if the overall general structural is similar. A recent appeal decision illustrates this point well.

The Electrode Tip Impact Tool Case

The application at issue involved an electrode tip impact tool—a device used to mount an electrode tip to a welding robot. The claim required, among other things, that the head of the tool has a first length greater than its height. Appeal 2025-000177, Application 17/580,083

Claim 1:

An electrode tip impact tool for mounting an electrode tip to a welding robot, the impact tool, comprising:
a handle;
a head at an end of the handle, the head includes a first edge comprising a tip-receiving bore sized to receive an electrode tip and an opposite second edge comprising a raised ridge for striking the head with a hammer; and
a striking projection that extends outward from a flat surface of the raised ridge completely surrounding the striking
projection;
wherein the handle extends outward from a bottom of the head, the bottom extending between the first and second edges and having a first length in a direction perpendicular to the handle that is greater than a height in a direction parallel to the handle of the first and second edges, the head having a top that is opposite of and parallel to the bottom extending between the first and second edges, the tip-receiving bore extending inward from the first edge toward the raised ridge;
wherein the raised ridge and striking projection together extend outward from the second edge a second length in the direction perpendicular to the handle that is less than the first length of the bottom of the head.

The examiner seemed to place the burden of difference in function on the applicant:

The PTAB sided with the applicant. The Board accepted the applicant’s reasoning that changing the head’s relative dimensions would alter the striking function, and noted that the examiner had not adequately explained why the prior art as modified would still perform the same function. This is significant: the applicant did not rely on experimental data, declarations, or extrinsic evidence—just clear, plausible technical reasoning grounded in the device’s operation. The Board confirmed that because the examiner had not established any basis for finding that there was no change in function, the applicant’s plausible reasoning was sufficient.

This case underscores an important point: relative dimensions in claims are often anything but “mere”. When dimensional differences impact how a device performs, they can form the basis of a strong argument against an obviousness rejection—even without expert evidence.

A few practical pointers:

• Anchor the dimensional limitation in function. Explain how the claimed proportion changes the way the device operates relative to the prior art, hopefully with support for such function in the specification.
• Point out examiner gaps. If the examiner hasn’t explained why the prior art, as modified, would still perform the same function, highlight that deficiency.
• Declarations still might be prudent. While expert evidence may not be required, well-reasoned technical arguments supported by a declaration can carry ever more weight.

So the next time you see “mere change in proportion” cited in a rejection, don’t let it slide.