The D4C1720 is a roller lever limit switch from Omron's D4C series, built for position sensing in wet or dusty environments. It's a momentary-action SPDT switch with a side-mounted roller lever actuator, rated for 5 A at 250 V AC (resistive) and 4 A at 30 V DC. The IP67 rating means the switch body and actuator are sealed against dust and temporary submersion — out here in the grease, that's what keeps a limit switch from getting killed by washdown or coolant spray. The 16.4 ft SJT(O) cable comes attached, so you don't need to add a connector or worry about the boot leaking. Approvals include UL Listing, CSA, CE, and CCC, so it's accepted across North American and international panels without extra paperwork.
The 5 A AC-1 resistive rating is the number that governs most panel applications — it's the continuous current the contacts can make and break on a resistive load. The 4 A DC rating at 30 V is for low-voltage control circuits; don't try to switch a 48 V DC solenoid without checking the DC derating curve, because inductive loads will arc longer at higher voltages. The roller lever has a 0.68 in roller diameter on a 0.28 in width, side-mounted with fixed arm adjustability. Pretravel is 25°, overtravel 40°, differential travel 3°. That's a fairly generous operating window — good for applications where the cam or dog isn't perfectly repeatable, like conveyor diverters or packaging machine gates. Body is aluminum, arm is aluminum, roller is stainless steel. The stainless roller matters if you're in a washdown zone — it won't rust and gall on the cam surface. No boot on the actuator, so if you need a sealed plunger for high-pressure spray, you'd want a different variant with a boot.