This is a foundation component: a 2.5″ round aluminum plate with the industry-standard 4-hole AMPS pattern (plus an additional 3-hole 120° pattern), topped with a heavy-duty C Size ball. Bolt it directly to a flat surface as a drill-down base, or use it as an adapter that lets any AMPS-pattern device holder connect to a C Size RAM double-socket arm.

Features

• 2.5″ round plate connects to RAM device holders containing the universal AMPS hole pattern
• Included C Size 1.5″ RAM rubber ball allows connection to any C Size RAM double-socket arm; ball-and-socket technology allows near-infinite adjustability
• Made of powder-coated, marine-grade aluminum for durability and reliability in the most demanding environments
• Backed by a lifetime warranty

How RAM's modular system works

Every RAM mount is built from up to three parts that click together, and the same parts mix and match across RAM's entire catalog:

• A base — clamps, bolts, or straps onto the vehicle (a rail, a roll bar, a dash, a windshield, or a device's own housing).
• An arm — connects two RAM balls together. It locks at any angle, so once mounted you can tilt, rotate, and reposition the device freely, then lock it firmly by hand.
• A cradle or holder — grips the specific device (tablet, phone, GPS unit, camera).

Not every product includes all three parts — some are just the base, some bundle a cradle, some are a complete kit. Further down this page we say plainly which parts this specific product includes, so you know exactly what you're getting and what, if anything, you'd need to add.

The ball size determines what it can carry. RAM uses five ball sizes, each rated for a different weight and duty class:

• A Size — rarely used; costs more to make than B Size but carries less. Reserved for small, low-profile items like security cameras where bulk matters more than capacity.
• B Size (1″ ball) — RAM's most common size, standard duty. This is what RAM recommends for phones, GPS units, and light tablets in normal use.
• C Size (1.5″ ball) — heavy duty. Used for larger tablets, handheld computers/scanners, CB radios, and anything mounted somewhere that gets a lot of vibration or shock — exactly the case in a tractor, ATV, or UTV cab.
• D and E Size — reserved for large monitors and specialist/military equipment; rarely needed outside those cases.

This product uses a C Size ball (1.5″ / 38 mm). RAM builds the round plate in both B Size and C Size — this is the C Size version, meant for larger tablets, handheld computers, and equipment that will see real vibration in a vehicle cab. If you're mounting something lighter, like a phone or a small GPS unit, our B Size version (RAM-B-202U) is the lighter, more compact match.

Rule of thumb: if the mount will live somewhere that's frequently jostled, vibrated, or under constant load — an off-road vehicle like a tractor, ATV, or UTV — RAM recommends stepping up to the larger ball size for extra stability, even if a lighter mount would technically hold the device's weight.

Round plate or diamond plate — what's the difference? Both carry the same C Size ball and both use the AMPS mounting standard, but the footprint differs. This round plate is 2.5″ in diameter with a 4-hole AMPS pattern (1.181″ × 1.496″) plus an additional 3-hole 120° pattern (1.812″ diameter) — more mounting holes means more holders are compatible out of the box, and the wider base spreads load over a larger area. RAM's diamond plate (see our RAM-238U) has a smaller 2.43″ × 1.31″ footprint with a single 2-hole pattern (1.912″ spacing) — it's lighter and fits tighter spaces, at the cost of a narrower range of compatible holders. If you already know which cradle you're pairing this with, check which pattern it uses; if you're not sure, this round plate's wider compatibility is the safer default.

No tools required, on purpose. RAM arms are designed to be tightened by hand only — there's no official torque spec, because the ball-and-socket joint is meant to be adjustable in the field without a wrench. If hand-tightening doesn't hold your device firmly, that's usually a sign the ball size is undersized for the device — sizing up solves it, rather than over-tightening.

Aluminum or composite — both are built for the outdoors. RAM mounts are made from marine-grade aluminum or high-strength composite, interchangeably depending on the part; both carry a lifetime warranty and similar weight ratings. Aluminum's powder-coat finish handles rough vibration and shock slightly better; composite skips the paint entirely, so it has nothing to chip, and is often preferred in high-corrosion or salt-air environments. Neither choice is "worse" — it's a trade-off between finish and environment.

Specifications

Frequently asked questions

What does this base actually attach to?
You bolt the round plate directly to a flat surface (a tractor cab wall, a bracket, an equipment panel) using the holes in the plate, or you attach it as an adapter to a device or holder that already has a matching AMPS hole pattern on its back.

Does it include an arm or a device holder?
No — this is the base plate and ball only. Pair it with a C Size RAM double-socket arm and an AMPS-compatible cradle (for a tablet, phone, or terminal) to complete the mount. Ask us and we'll match the right combination to your device.

Do I need C Size or would B Size work?
If you're mounting a larger tablet, handheld computer, or anything that will sit in a tractor, ATV, or UTV cab and take real vibration, go with this C Size version. For a phone or a small GPS unit in normal use, our lighter B Size plate (RAM-B-202U) is the better match.

Is drilling required?
Yes — this base is meant to be bolted or screwed down, either directly to a flat surface or to a matching AMPS device holder. Common screw sizes are #8, #10, M4, or M5; if you're pairing it with a RAM holder, the holder ships with the hardware it needs.

Does it have a threaded hole on the bottom for a bolt?
No, there's no female threaded hole — mounting is done through the plate's own holes with screws or bolts from underneath.

What's the difference between this and the diamond plate version?
See the section above — same C Size ball, but this round plate has more mounting holes and a wider footprint for broader holder compatibility, while the diamond plate (RAM-238U) is smaller and lighter.