Plain black webbing, 35mm wide, with polished silver-tone clips at each end. The X back style keeps the straps sitting square across the shoulders, and the adjusters let you set the drop once and leave it. Made in Britain.
Black is the easy choice: it disappears under a waistcoat and looks right with morning dress or black tie, but works just as well under a plain business jacket. The clips fasten to the waistband, so no buttons are needed inside the trousers.
They arrive in a presentation gift box, which makes them straightforward to hand over on a wedding morning. Check the waistband is firm before you clip on, and set both sides to the same length.