D38999/26WC98SN is a MIL-DTL-38999 Series III circular connector designed for rugged signal, power, control, and optical applications in aerospace, defense, and marine environments. The connector features a scoop-proof, triple-start, self-locking threaded coupling mechanism with multiple shell sizes ranging from 09 to 25, each with corresponding accessory threads (M12 x 1.0 to M37 x 1.0), mating threads (0.6250 to 1.6250 inches), and jam nut threads (M17 x 1.0 to M44 x 1.0). The connector is available in aluminum, stainless steel, and composite shell materials with mass ratings from 9 g to 143 g depending on shell size and material selection. This connector withstands extreme temperatures from -65°C to +200°C, maintains airtight/vacuum sealing at less than 1×10?7 cm³/s at 14.7 psi, and demonstrates excellent resistance to fluid, corrosion, and high vibration. Applications include sensors, fuel tank systems, down-hole drilling equipment, engine accessories, pyrotechnic equipment, vacuum chambers, optical devices, missiles, avionics, and sealed environments requiring reliable environmental protection.