Ball size controls the mounting system
B Size arms fit B Size balls, C Size arms fit C Size balls, and so on. Different ball-size families do not connect directly unless a suitable adapter is used.
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The RAM® system, made simpler
Which RAM® ball size do I need?
Choose a ball-size family for the weight and conditions, then choose an arm length within that same family. This guide makes both decisions easier.
Step 1
Compare all five RAM® ball sizes
The official proportional round-ball-base drawings make the physical jump between each family easier to recognise.
Quick start
Find your likely starting size
Standard use
Normal roads and stable environments
Most everyday car, desk, indoor and low-vibration applications. B Size is RAM's usual starting point for standard-duty use.
Heavy-duty use
Movement, vibration or repeated force
Off-road vehicles, choppy water, turbulence and other regularly jostled environments. Use the lower heavy-duty capacity and consider C or D Size.
Most common for phones
B Size
25.4 mm / 1 inch ball
- Standard use
- Holds up to 0.91 kg / 2 lb
- Heavy-duty use
- Holds up to 0.45 kg / 1 lb
Phones, GPS units, lightweight cameras and small tablets in lighter-duty setups.
More holding power
C Size
38.1 mm / 1.5 inch ball
- Standard use
- Holds up to 1.81 kg / 4 lb
- Heavy-duty use
- Holds up to 1.36 kg / 3 lb
Tablets, scanners, medium-duty vehicle mounts and many work or marine setups.
Heavy-duty system
D Size
57.2 mm / 2.25 inch ball
- Standard use
- Holds up to 2.72 kg / 6 lb
- Heavy-duty use
- Holds up to 2.27 kg / 5 lb
Marine electronics, larger screens, heavier equipment and demanding vehicle applications.
Specialist applications
E Size
85.9 mm / 3.38 inch ball
- Standard use
- Holds up to 6.80 kg / 15 lb
- Heavy-duty use
- Holds up to 4.54 kg / 10 lb
Specialist heavy equipment and unusual applications requiring very high holding power.
Identify the size from the SKU
The letter after RAM usually reveals the family
There are exceptions, but these prefixes are a reliable first check. C Size is unusual because it normally uses RAM- with no size letter.
RAM-A-RAM-B-RAM-RAM-D-RAM-E-
Step 2
Choose your socket-arm length
Select the ball-size family you are building. The measurements update without forcing a wide comparison table onto mobile.
B Size arms connect to B Size ball components.
Short arm
Overall length: 61.5 mm / 2.42 in
Socket-to-socket: 44.5 mm / 1.75 in
Compact, low-profile positioning.
Medium arm
Overall length: 94.7 mm / 3.73 in
Socket-to-socket: 76.2 mm / 3.00 in
Balanced reach for everyday setups.
Long arm
Overall length: 152.4 mm / 6.00 in
Socket-to-socket: 134.9 mm / 5.31 in
More reach, with greater leverage.
Overall length
The complete end-to-end length of the arm.
Socket-to-socket
The working distance between the centres of the two ball sockets.
Ball size does not confirm device fit
Ball size tells you which mounting components connect together. It does not tell you whether a holder fits your phone or tablet.
Find a compatible holderReal help is still here
Still unsure?
Tell us the device, its approximate weight, where it will be mounted and how it will be used.
Ball illustrations, naming conventions and application guidance are based on the official RAM Mounts ball-size guide. Published capacities are selection guidance. Device weight, mounting angle, arm length, vibration and environment also matter.