I have an iPhone X and simply pair it with a Sennheiser.

This is when you attract boomer comments, comes to show of age because it turned a little yellow?

All Sennheiser cables are the same which is a 2.5mm to 3.5mm headphone jack but they’ve a particular twist & turn proprietary hook that doesn’t allow third-party ones (which I found out the hard way) to enter the headphone side (2.5mm) without using theirs. The cables fray like Apple’s lightning cable and are of shit quality as well while priced a premium.

Why are you using decimals?