English to Spanish Tech/Engineering Mechanics / Mech Engineering technical

Hello,

What is the equivalent of "styli" in the following sentence:

"Similarly, bottle styli were prepare by cutting 7 x 7 mm bottle sections and mounting onto square stainless steel backing plates.
Mar testing was conducted on a Scratch 4 Machine from Surface Machine Systems.
In this test the styli were slid across rectangular test section at a velocity of 50 mm/s for a length of 100 mm under a progressively increasing load where the starting load was 1 newton and the ending load was 100 newtons.
The sliding action of the styli left a mar damage field of increasing intensity, due to the progressively increased load, along the test specimen."

Thanks!