Jagwire M5 Index Barrel Adjuster - Black - Each

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! -)