Turns out the round 1x1 plate with a plain stud is slightly thicker than the one with a hollow stud.

The rate of the discrepancy seems to be roughly a half-plate for every 33 plates. Update : Given the input of several commenters who attempted to replicate this phenomenon, it appears this is a batch-specific issue likely caused by an overworn factory mould. Therefore, this observation should not be extrapolated to all pieces of those shapes - even if it may be somewhat common. submitted by /u/Serendipitian [link] [comments]