A rail kit holds a UPS, a battery pack or other equipment in a 19-inch rack. Rail kits are made for specific equipment and for a specific rack type, so a kit that fits one UPS family may not fit another.
1. Start from the exact equipment model
Manufacturers list their rail kits per product family. For example, APC's SRTRK4 is a 19-inch rail kit for Smart-UPS SRT 1 to 3 kVA models, while SRTRK3 is a 2-post mounting kit for the same family [1]. Read the model on the equipment label and check the kit's compatibility list.
2. Check the rack type: 2-post or 4-post
A 4-post kit supports the equipment front and rear; a 2-post kit mounts it at the centre posts. Manufacturers sell separate kits for each (APC SRTRK3 for 2-post, SRTRK4 for 4-post on Smart-UPS SRT; Eaton RK2PC for 2-post on its online UPS) [1][2]. Heavy UPS and battery packs usually call for 4-post support.
3. Check the depth
Measure the distance between the front and rear mounting rails of your rack. Rails adjust over a range: APC's Smart-UPS 4-post rails extend up to 36 inches (91.44 cm), and the rack's own rails may need adjusting for a proper fit [3]. Depth adapter kits exist for racks outside a kit's range [2].
4. Check the load
A UPS with internal batteries is heavy. Mount it low in the rack, and use the rails listed for that model, not a generic shelf, unless the manufacturer lists the shelf for it.
Not sure which kit fits?
Send us the equipment model, the rack model (or its post type and rail-to-rail depth) and where in the rack it goes. We will confirm the matching kit before you order. Browse rack and mounting kits.
Sources: [1] Schneider Electric product pages SRTRK4 and SRTRK3 (se.com, read 2026-09-29). [2] Eaton product pages RK2PC and SRRAILDPTH2U (tripplite.eaton.com, read 2026-09-29). [3] Schneider Electric FAQ000268228, "What is the max depth of the APC Smart-UPS 4 Post Rail Kit?" (se.com, read 2026-09-29).