The Delmhorst 2497/A-100/4 are contact pins used on many meters and the 2-E Electrode and come in a package of 4. They penetrate up to 5/16".
These pins are standard equipment on the Delmhorst J-series meters, RDM-3, TechCheck, paper meters, BD-series meters, and the 2-E electrode. They can also be used on the 4-E Electrode, which ships standard with 11/16" penetration pins.