These screws have a nib machined on the end so that when the end of the screws becomes galled over time, one can still unwind and disengage the screw from the socket block.
The nib also provides a positive and convincing engagement with your arm.
We have stainless steel and high-tensile available.
The stainless steel won’t rust, but being grade 304 (surgical grade steel), It is a little more malleable and will tend to wear down a little faster than the high-tensile screws.
On the other hand, the high-tensile screws (which our industry has been using for decades) are not subject to wearing down so fast but can be subject to surface rust in general environments and more so in tropical and higher humidity locations. So, to minimise this, we have treated them with a black oxide coating.