These screws have a rubber O-ring underneath the head to stop leaks and keep impurities out. The dimensions satisfy ISO 4762 (formerly DIN 912) or ASME B18.3 requirements. Under the head, the length is measured.

18-8 stainless steel screws may be slightly magnetic and have strong corrosion resistance.

In addition to having superior resistance to chemicals and sea water, 316 stainless steel screws are more corrosion resistant than 18-8 stainless steel screws. They might have a slight magnetic field.

O-ring screws are resistant to abrasive and damp conditions.

Screws with an O-ring resist oil and chemicals.

Silicone O-ring screws withstand corrosion from saline water and work well in a variety of temperatures.

If you are unsure of the pitch or threads per inch, go with the industry standard coarse thread screws.