Sleeve Nuts are available in a variety of forms.
Countersunk flat head allen socket and slotted oval head sleeve nuts recess into the surface of the work whereas ultra low profile head allen socket sleeve nuts sit proud of the work surface after install.
A4 / 316 Stainless Steel fasteners are “marine grade” corrosion resistant; suitable for salt water applications. A4 fasteners also offer increased resistance to chemicals when compared with A2 stainless fasteners.