Silver metal rectangular adjuster 25mm.
The rectangular adjuster can be used with the rectangle rings to make a cross body bag strap adjustable! -
https://www.owlandsewingcat.com/products/metal-rectangle-ring-25mm-used-for-the-3-way-bag
Find the 3 way bag sewing pattern here - https://www.owlandsewingcat.com/products/three-way-bag-pattern