Usually titanium, but yeah sometimes medical stainless steel. Both are non-ferromagnetic, especially titanium. These balls look like they could well be normal steel or any other metal. Also, implants - unlike these metal balls - are usually screwed firmly into your bones. So yeah, implants should be mostly fine on MRI. Loose balls of dubious metal? Wouldn’t advise it. Keep in mind MRIs are literally powerful enough that metals in tattoo ink can even be an issue - which the article you linked mentions itself.

In general, metallic orthopedic implants are not affected by MRI.

This isn’t an implant though. Massive difference.

Or the twist erase

Yeah but with mechanical pencils you can buy one and have it for years, only just buying the occasional pack of leads… Saves the trees ¯_(ツ)_/¯

I have two twist-erase 3’s and I’ve never looked back. I love them so much.

*Blimey

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