Do RAM ball sizes fit different socket arms?
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
RAM® Mount ball sizes, weight capacity & arm lengths
Compare RAM Mount ball sizes in mm and inches, check weight capacities, then choose a socket-arm length that puts your device where you need it.
Step 1
RAM® Mount ball size chart
Compare A, B, C, D and E Size balls. Use the drawing for proportions and the table for exact diameters and weight capacities.
| Ball size | Diameter | Standard use | Heavy-duty use |
|---|---|---|---|
| A Size | 14.3 mm / 9⁄16 in | 0.23 kg / 0.5 lb | Not specified |
| B Size | 25.4 mm / 1 in | Holds up to 0.91 kg / 2 lb | Holds up to 0.45 kg / 1 lb |
| C Size | 38.1 mm / 1.5 in | Holds up to 1.81 kg / 4 lb | Holds up to 1.36 kg / 3 lb |
| D Size | 57.2 mm / 2.25 in | Holds up to 2.72 kg / 6 lb | Holds up to 2.27 kg / 5 lb |
| E Size | 85.9 mm / 3.38 in | Holds up to 6.80 kg / 15 lb | Holds up to 4.54 kg / 10 lb |
Capacities are up to the values shown. Use the lower heavy-duty rating for vibration or rough conditions. Check the complete setup and the exact component specifications before ordering.
Quick start
Which RAM ball size do I need?
B Size vs C Size: what is the difference?
B Size: 25.4 mm (1 inch) ball. The smaller option, commonly used for phones, GPS units and lightweight devices.
C Size: 38.1 mm (1.5 inch) ball. Higher published weight capacity for heavier devices. Check the standard-use or heavy-duty rating for your setup.
The sizes do not fit directly together: a C Size arm will not fit B Size balls. When upgrading, match the base ball, both arm sockets and the holder’s ball or ball adapter.
Standard use
Standard-use weight capacity
Everyday car, desk, indoor and low-vibration applications. Check the standard-use rating for the appropriate ball family.
Heavy-duty use
Heavy-duty weight capacity
Off-road vehicles, choppy water, turbulence and other regularly jostled environments. Use the lower heavy-duty capacity and reassess the ball family for the complete setup.
These are published selection ratings, not a guarantee for every complete mount. Check the exact base, holder and mounting surface too. Weigh the device with its case and account for supported accessories; stay within the lowest applicable component limit.
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.
Rugged 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 / nominal 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
C Size commonly uses RAM- with no size letter. Read the whole part number: RAM-B-201U-C is a long B Size arm, not a C Size arm. Confirm the stated ball/socket size before ordering.
RAM-A-RAM-B-RAM-RAM-D-RAM-E-
Step 2
RAM® Mount arm lengths: short, medium or long?
Select your ball family to compare exact arm models. Choose the shortest arm that achieves the position and clearance you need.
Short: compact positioning.
Standard / medium: extra clearance and reach.
Long: further reach, with greater leverage.
Length does not change the ball family or automatically raise its weight rating. “Short” and “medium” are relative to each family, not universal measurements. “Standard / medium” describes arm length, not the standard-use load rating.
Comparing a different family does not change the size of the balls you already own.
B Size arms
B Size arms fit B Size balls. 25.4 mm / 1 inch
Short arm
RAM-B-201U-A
Overall length: 61.5 mm / 2.42 in
Socket-to-socket: 44.5 mm / 1.75 in
Keeps the device close to the base. Check clearance around the holder.
View B Size short armStandard / medium arm
RAM-B-201U
Overall length: 94.7 mm / 3.73 in
Socket-to-socket: 76.2 mm / 3 in
A middle length for positioning and clearance. Compare the exact dimensions within this ball family.
View B Size medium armLong arm
RAM-B-201U-C
Overall length: 152.4 mm / 6 in
Socket-to-socket: 134.9 mm / 5.31 in
Reaches further from the base. Recheck load and leverage in demanding conditions.
View B Size long armExact-model specifications: RAM-B-201U-A · RAM-B-201U · RAM-B-201U-C.
C Size arms
C Size arms fit C Size balls. 38.1 mm / 1.5 inch
Short arm
RAM-201U-B
Overall length: 90.4 mm / 3.56 in
Socket-to-socket: 63.5 mm / 2.5 in
Keeps the device close to the base. Check clearance around the holder.
View C Size short armStandard / medium arm
RAM-201U
Overall length: 144.5 mm / 5.69 in
Socket-to-socket: 118.4 mm / 4.66 in
A middle length for positioning and clearance. Compare the exact dimensions within this ball family.
View C Size medium armLong arm
RAM-201U-D
Overall length: 231.8 mm / 9.125 in
Socket-to-socket: 203.2 mm / 8 in
Reaches further from the base. Recheck load and leverage in demanding conditions.
View C Size long armExact-model specifications: RAM-201U-B · RAM-201U · RAM-201U-D.
D Size arms
D Size arms fit D Size balls. 57.2 mm / 2.25 inch
Short arm
RAM-D-201U-C
Overall length: 129.5 mm / 5.1 in
Socket-to-socket: 91.4 mm / 3.6 in
Keeps the device close to the base. Check clearance around the holder.
View D Size short armStandard / medium arm
RAM-D-201U
Overall length: 214.4 mm / 8.44 in
Socket-to-socket: 174.8 mm / 6.88 in
A middle length for positioning and clearance. Compare the exact dimensions within this ball family.
View D Size medium armLong arm
RAM-D-201U-E
Overall length: 329.7 mm / 12.98 in
Socket-to-socket: 289.8 mm / 11.41 in
Reaches further from the base. Recheck load and leverage in demanding conditions.
View D Size long armExact-model specifications: RAM-D-201U-C · RAM-D-201U · RAM-D-201U-E.
E Size arms
E Size arms fit E Size balls. Nominal 85.9 mm / 3.38 inch
Short arm
RAM-E-201U-D
Overall length: 185.7 mm / 7.31 in
Socket-to-socket: 126.4 mm / 4.975 in
Keeps the device close to the base. Check clearance around the holder.
View E Size short armStandard / medium arm
RAM-E-201U
Overall length: 320.7 mm / 12.625 in
Socket-to-socket: 250.8 mm / 9.875 in
A middle length for positioning and clearance. Compare the exact dimensions within this ball family.
View E Size medium armExact-model specifications: RAM-E-201U-D · RAM-E-201U.
This guide lists selected models, not every specialist arm or configuration. Contact us if you need a different option.
A Size arms
A Size arms fit A Size balls. 14.3 mm / 9/16 inch
Standard / medium arm
RAM-A-201U
Overall length: 53.6 mm / 2.11 in
Socket-to-socket: 42.4 mm / 1.67 in
A middle length for positioning and clearance. Compare the exact dimensions within this ball family.
RAM model specificationsLong arm
RAM-A-201U-B
Overall length: 90.4 mm / 3.56 in
Socket-to-socket: 79.2 mm / 3.12 in
Reaches further from the base. Recheck load and leverage in demanding conditions.
RAM model specificationsExact-model specifications: RAM-A-201U · RAM-A-201U-B.
This guide lists selected models, not every specialist arm or configuration. Contact us if you need a different option.
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.
Socket spacing is not the final distance from the mounting surface to your screen. The base and holder add offsets, and the arm angle changes horizontal and vertical reach.
How to measure a RAM socket arm and check its position
- Identify where the base ball will sit, including the offset from its attachment point.
- Hold the device where you want it. Check visibility, controls, cables and room to insert or remove it. Keep vehicle installations clear of airbags and essential sight lines.
- Allow for the holder's ball position. Compare the required ball-centre spacing with the socket-to-socket measurements above.
- If the position calls for a long arm in a demanding application, ask us to check the complete setup before ordering.
Already have a RAM mount? Identify what you can reuse
Measure the ball across its widest point, not the outside of the socket arm or base plate. Match it to the ball diameters above.
If the existing family remains suitable for the load and conditions, changing arm length within that family may solve a height or reach problem without replacing everything. Changing to a larger-family arm alone will not make smaller balls fit.
Two customer examples: when shorter or longer made sense
These published, verified customer reviews illustrate positioning choices. They are individual experiences, not load tests or guaranteed fit recommendations.
Shorter solved a height problem
A BMW R1200RT owner reported that the regular arm positioned the phone too high.
“I then changed it over for the short clamp and the working height of the phone is perfect.”
RAM-B-201U-A review, 22 August 2023.
Longer improved reach
A customer using a long-arm suction mount needed reach over a wide dashboard.
“Long arm works great when mounted to windscreen set back over a wide dashboard, providing easier reach”
RAM-B-166-C-PD4U review, 1 January 2022.
Will my phone or tablet fit the holder?
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 holderWatch: RAM ball sizes and socket arms
See how the RAM ball-and-socket system works in these manufacturer overviews.
Ball & Socket Sizes — RAM® Mounts
Watch on YouTube
Double Socket Arms — RAM® Mounts
Watch on YouTube
Use these videos to understand the components. Check the chart above for standard-use and heavy-duty capacities, and the arm comparisons for the measurements of your exact model.
Real help is still here
Still unsure?
Tell us your device and case, supported weight, mounting location and what needs to change: height, reach, clearance or load. Include existing part numbers or a photo if available.
Ball illustrations, naming conventions and application guidance are based on the official RAM Mounts ball-size guide. Individual arm specifications checked 9 September 2026. Inch measurements are source values; metric conversions are rounded. Where a general table differs, the individual model specification is used. Capacities are selection guidance; the complete installation must suit the load and conditions.