Question regarding 16610 links

[Toutoune]

Hello everyone,

I looked online for the answer to the following question but wasn’t able to find any explanation so I decided to come up here and ask if somebody knew.

Apologise in advance if the answer is obvious and thus the question stupid but the itch to know is too important!

16610 with 93250 bracelet code (it might apply to some other references and/or bracelets but for me it is this one): why do some links have a « circle » on the inside whereas others don’t??

T.