References in this pack (guard razor knives) are in principle for a 31B. Featuring a 31S and not having found the reference that corresponds I tried this combi-pack 31B after taking care to visually compare the elements of my razor with photos of the product. Banco! The elements correspond perfectly! So it is good to know for the owners of 31S (370 Series 3 - 5738 type). In addition, super fast delivery by Amazon ...