This is an M3 ruby ball stylus #A-5000-3554 with stainless steel stems.

Straight styli are designed to inspect simple features where direct, unobstructed contact with a measured surface is possible. A stainless steel stem offers excellent rigidity and is ideal for applications where weight is not critical. Ruby is regarded as the industry standard for stylus tips. It is one of the hardest materials available and suitable for most applications. Due to adhesive pickup, ruby tips are not recommended for scanning aluminium parts.