The Fluke TP4 is a Test Probe, Slim-Reach 4MM Diameter.

Safety designed probes with slender, Slim-Reach bodies and stainless steel tips. Effective for reaching closely-spaced deep test points or recessed terminals. All Slim-Reach probes are rated for 10 amps, and may be used in 1000V CAT III environments. 4 mm (0.16 in) diameter tip designed to fit securely in IEC electrical wall sockets.