The following is the Collectors' Clearinghouse column from the Dec. 12, 2016, issue of Coin World:

A collar break (“collar cud”) is expected to appear in the same spot on the edge of every coin struck within that collar. Such is indeed the case for every known 20th and 21st century collar break — except one. A large series of 2002-P Kennedy half dollars shows a collar break that steadily changes its position relative to the design. This presumably indicates that the collar itself was rotating.

This rotating collar break was independently discovered by Gary W. Alt (Collectors’ Clearinghouse, Jan. 6, 2003) and William “Ed” Eubanks. Eubanks published his analysis in the July/August 2003 issue of Errorscope. Eubanks noticed the defect while digging through five Mint-sewn bags of 2002-P half dollars. Close to 300 of the original 500 coins showed a “nub” on the edge. The nub was, of course, a small collar break. Eubanks made a careful study of the 261 coins that he retained.

The collar break is more precisely described as a “collar chip.” The upper half of one of the ridges on the working face of the collar broke off, allowing coin metal to flow into the resulting void. The collar chip is located next to the reverse face, which was struck by the hammer die.

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Eubanks tracked the movement of the collar break through three die changes and one or more die stages within each die pairing. The movement was consistently clockwise and completed a full 360 degree circle plus another 45 degrees (a total of 405 degrees).

Die pair 1 has five die stages through which the collar break travels clockwise from 6:00 to 3:00 (270 degrees). Die stage 1/1 is defined by a small die gouge that extends from the top of the first 0 of the date. In this die stage the collar break can be found anywhere between 6:00 and 7:30 (obverse clock position). Fifty-five of Eubanks’ total sample of 261 coins fall into this die stage.

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Die stage 1/2 is defined by the addition of two die cracks. One extends from the eagle’s right wing tip to the design rim; the other extends from Kennedy’s neck toward the design rim. During this die stage the collar break occupies a position anywhere from 7:30 to 9:00. Twenty-two coins fall into this die stage.

In die stage 1/3, both of the afore-mentioned die cracks lengthen. Within this die stage the collar break occupies a variable position between 9:00 and 10:30. Five half dollars occupy this die stage.

Die stage 1/4 is identified by the presence of a small die crack that extends down from the eagle’s central tail feather. During this stage the collar break occupies a position anywhere from 10:30 to 1:30. Twenty-four of the coins fall into this die stage.

In Die stage 1/5, the die crack that appeared in the previous stage lengthens and almost touches the star located directly beneath it. During this die stage the collar break occupies a position anywhere from 1:30 to 3:00. Three coins are in this die stage.

After this the obverse die is removed and replaced with a new die. The new obverse die shows a “bubbly imperfection” in the field, just below Kennedy’s neck and just above the T in TRUST. During this die stage (2/1) the collar break occupies a variable position between 3:00 and 4:30. Sixty-nine coins are contained within this die stage.

Die stage 2/2 features the addition of a die crack that extends from the point of Kennedy’s neck. During this die stage the collar break occupies a position anywhere from 4:30 to 6:00. Eighty coins populate this die stage.

After this both dies are replaced with new dies. Only one die stage is recognized, naturally defined by entirely new die markers. In this die stage (3/1) the collar break occupies a variable position between 6:00 to 7:30. Only three coins reside within this die stage.

It’s not at all clear why movement of the collar break is slow, steady, and consistently clockwise. Hundreds of thousands of half dollars were presumably struck during the three die pairings, so movement after each strike was likely microscopic.

It’s also not clear if the entire collar was rotating or just the working face. Some collars have a ceramic or tungsten carbide steel lining that can theoretically separate from the surrounding, softer die steel. I have no reports of such linings in collars designed to strike reeded coins, but neither can I exclude this possibility.

Rotating collar breaks are known from the 19th century. In the April 1997 issue (#11) of the specialty journal 2Times, Frank Leone discusses a rotating collar break in a sample of six 1864 2-cent coins that moves through 90 arc degrees (6:00 to 9:00). Leone also finds evidence of a rotating collar break in an 1865 Indian cent and other denominations going back to 1836.