A field device assembly includes a housing body, a first circuitry subassembly mounted to the housing body and positioned at least partially within the housing body, a first cover chassis having a shoulder, mating flame path restricting structures positioned on the first cover chassis and the housing body, a first threaded collar configured to fit about the first cover chassis and to permit rotation relative to the first cover chassis, and a second circuitry subassembly secured to the first cover chassis. The first threaded collar is threadably engaged with the housing body, and includes an engagement structure engaged with the shoulder of the first cover chassis to secure the first cover chassis to the housing body. The second circuitry subassembly includes an electrical connector configured for linear insertion engagement with a mating electrical connector within the housing body to electrically connect the first and second circuitry subassemblies.