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Really Right Stuff B2-mAS Screw-Knob Clamp with 1/4"-20 Screw (38mm)

BH #REB2MAS • MFR #B2-MAS
14 reviews
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Really Right Stuff B2-mAS Screw-Knob Clamp with 1/4"-20 Screw (38mm)
Key Features
  • Arca-Type Compatible Clamp
  • Laser-Engraved Scale
  • CNC Machined 6061-T6 Aluminum
  • Type II Black Anodized Finish
This B2-mAS Screw-Knob Clamp from Really Right Stuff is designed to mount to the top of tripods, monopods, or video fluid heads that do not have a quick release system. The clamp is CNC machined 6061-T6 aluminum and has a black anodized type II finish. It features a laser-engraved scale in 1mm increments for precise positioning. The screw-knob clamp will mount to any tripod, monopod, or head with a 3/8"-16 screw, or a reducer bushing can be utilized to fit 1/4"-20 studs. The base of the clamp features a rosette design for secure mounting to compatible ball heads and other devices, and will prevent twisting at the coupling point between the clamp and head over time. A legacy tongue-and-groove adapter is available separately.
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Really Right Stuff B2-MAS Overview

This B2-mAS Screw-Knob Clamp from Really Right Stuff is designed to mount to the top of tripods, monopods, or video fluid heads that do not have a quick release system. The clamp is CNC machined 6061-T6 aluminum and has a black anodized type II finish. It features a laser-engraved scale in 1mm increments for precise positioning. The screw-knob clamp will mount to any tripod, monopod, or head with a 3/8"-16 screw, or a reducer bushing can be utilized to fit 1/4"-20 studs. The base of the clamp features a rosette design for secure mounting to compatible ball heads and other devices, and will prevent twisting at the coupling point between the clamp and head over time. A legacy tongue-and-groove adapter is available separately.

  • Arca-type compatible clamp
  • Adds quick release functionality to a tripod or monopod
  • CNC machined 6061-T6 type II anodized black aluminum
  • Laser-engraved scale in 1mm increments
  • Rosette style mounting base
UPC: 818413023000

Really Right Stuff B2-MAS Specs

Quick Release Plate
Mounting
1x 1/4"-20 Female
Assembly
Plate Locking Method
Screw Knob
General
Quick Release Plate Type
Arca-Type
Quick Disconnect System
No
Bubble Level
Yes
Materials
Aluminum
Dimensions
2.9 x 1.5 x 0.6" / 7.32 x 3.8 x 1.5 cm
Weight
2.3 oz / 65.2 g
Packaging Info
Package Weight
0.2 lb
Box Dimensions (LxWxH)
4.1 x 3.8 x 0.5"

Really Right Stuff B2-MAS Reviews

Very good RRS Quality

By Ted
Rated 5 out of 5
Date: 2026-03-31

I attached these (I have two) to my Manfrotto Befree 3-Way Live Heads to change the rail direction to perpendicular to the lens direction because my cameras either have an L-frame or a grip with perpendicular Arca rails. This is the easiest method to change that and RRS always makes quality gear.

Good product, as always, but warning.

By Michael
Rated 3 out of 5
Date: 2022-03-02

The device will not lie flat because of the knob. It will alter the clamping direction by 90 degrees. Make sure that what you attach it too provides adequate space for the knob.

See any errors on this page?

Can you use the Peak Design Quick release plate ...

Can you use the Peak Design Quick release plate on this?
Asked by: Stephen
Yes, the Really Right Stuff B2-mAS Screw-Knob Clamp with 1/4"-20 Screw (38mm) should be compatible with the Peak Design PL-S-3 Standard Plate (BH #PEPLS3), because the plate uses the same Arca-Type quick-release design.
Answered by: Paige K
Date published: 2024-10-06

Will this fit on the IFootage Cobra 3 C180F-P?

Will this fit on the IFootage Cobra 3 C180F-P?
Asked by: Joel
Really Right Stuff B2-mAS Screw-Knob Clamp has a 1/4"-20 female screw and iFootage Cobra 3 Carbon Fiber Monopod with Pedal-Release Mini Tripod Base has a 1/4"-20 Male screw so it should screw in. If you need any help, please feel free to start a live chat during business hours. An expert from our Pro-Photo department can virtually guide you over live video in the store. https://bhpho.to/3MLX2vU
Answered by: Samik G
Date published: 2023-05-18

Can this be used on the Manfrotto BeFree? Will ...

Can this be used on the Manfrotto BeFree? Will the legs still fold properly?
Asked by: Aaron
With a reducer bushing purchased separately you can fit it on the top of the quick release plate that comes with your tripod but if you do that you will have two different clamps. You may end up sometimes opening the wrong clamp accidentally. If you want an arca clamp to a Manfrotto Befree tripod I would recommend this adapter from Manfrotto. If you use this you will only have one clamp. Please make sure your tripod head is listed as compatible in this listing. It is small and shouldn't affect the folding of the legs. https://www.bhphotovideo.com/c/product/1484861-REG/manfrotto_msq6t_top_lock_travel_quick.html
Answered by: Daniel C
Date published: 2021-08-24

Can this be used on the Gitzo Mini Traveler?

Can this be used on the Gitzo Mini Traveler?
Asked by: Attila
The Really Right Stuff B2-mAS Screw-Knob Clamp with 1/4"-20 Screw (38mm) can be used with the Gitzo Mini Traveler.
Answered by: Lawrence C
Date published: 2023-08-21

question

Can this clamp be mounted on another clamp to be used to change the direction of the rail's orientation?
Asked by: Paul
Yes, this is possible, but depending on what equipment you plan to mount and the knob size on the other clamp, there could be interference, though many configurations should work.
Answered by: nh_to
Date published: 2019-02-06
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