Shoulder planes come in all shapes and sizes.
These are just a few of my favorite.
This gunmetal plane by John William Thackeray
of Leeds is over
a century old now and is my favorite 3/4" plane.
It squares and refined shoulders perfectly.
The infill is African ebony.
This is a 1" wide shoulder plane by Henry
Slater of London, 1868-1909.
Again, ebony was used for infill.
It has a "Three Shamrocks" Marples iron,
probably original to this plane.