Jagwire M5 Index Barrel Adjuster - Black - Each

I recommend this product

This was a replacement for an M5 downtube barrel adjuster that had seized up in its housing. Perfect fit. Don't throw away the metal clip, it's the alternative to the traditional spring on the original adjuster.

I recommend this product

These gear tension "thimbles" or adjusters worked a treat as replacements though sad to say there was nothing "super" about them other than they worked just fine to replace a pair that had seized in the down tube of a friend's elderly alloy Trek bike (neither WD40, a blow torch or stud extractors could remove the old ones - other than drill and re-tap the braze-ons!).
One thing that did make them so easy to refit was the spring retaining clip...do not throw away, a really useful bit of steel to have when serving a bike! -)