Open and frameless slip rings
Fabricast Brush-block slip rings
Separate rotor and brush-block slip rings with unobstructed 0.50, 1.00, 1.50 and 2.00 in through-bores for integration into the customer's own housing.
Key specifications
| Bore | 12.7–50.8 mm |
|---|
Summarised in our own words from United Equipment Accessories, Inc.'s published data; series maxima, individual models vary. Last checked 2026-10-30. Source 1
Notes on this data
Electrical ratings for the brush-block versions were not read.
Specify Motion is not affiliated with United Equipment Accessories, Inc.. Fabricast and Brush-block slip rings are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
Alternatives that meet or exceed these figures
Engineers often come to us with a Fabricast part number and leave with an alternative that is easier to source, quicker to deliver or a better fit for the machine. These 3 series from our supply network are the closest match on published figures.
Through-bore slip rings with a hollow centre so shafts, pipes or cables can pass through, carrying power, signal and fieldbus data. Standard bores run from 12.7 mm to 100 mm and custom bores are offered.
| Published maximum | Brush-block slip rings | ER Series Through Bore Slip Ring |
|---|---|---|
| Circuits | — | 24 |
| Current per circuit | — | 15 A |
| Speed | — | 300 rpm |
| Voltage | — | 380 V |
| Bore | 50.8 mm | 100 mm meets or exceeds |
Flat, disc-style slip rings for machines with little axial height but room radially, available with or without a through hole. They pass power alongside signals such as USB, Ethernet, audio and video.
| Published maximum | Brush-block slip rings | PR/PSR Series Pancake Slip Ring |
|---|---|---|
| Circuits | — | 30 |
| Current per circuit | — | 20 A |
| Speed | — | 100 rpm |
| Voltage | — | 380 V |
| Bore | 50.8 mm | 500 mm meets or exceeds |
Slip rings with dedicated 100M or Gigabit Ethernet channels alongside power and signal circuits, offered in solid-shaft and through-bore forms.
| Published maximum | Brush-block slip rings | Ethernet Slip Ring |
|---|---|---|
| Circuits | — | 100 |
| Current per circuit | — | 30 A |
| Speed | — | 300 rpm |
| Voltage | — | 240 V |
| Bore | 50.8 mm | 100 mm meets or exceeds |
Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
What an open and frameless slip ring is
An open or frameless slip ring is supplied as separate components, typically a ring assembly and one or more brush blocks, without its own housing or bearings. The machine builder mounts the rings on the rotating part and the brushes on the stationary frame, using the machine's own bearings to locate them. This lets the slip ring fit around large shafts, inside existing housings or in very short axial spaces. Designs range from precious-metal signal rings to heavy copper rings with carbon brushes for high current.
When engineers choose an open and frameless slip ring
Choose a frameless design when a housed unit will not fit, when the bore is very large or when the machine already has stiff bearings and a protected space to house the rings. It saves weight and length and avoids a second set of bearings fighting the machine's. The trade-offs are responsibility and risk: concentricity, runout, brush preload, sealing and contamination control all move to the machine builder. Plan assembly, setting and inspection procedures carefully.
How to specify the Fabricast Brush-block slip rings
Send these with your enquiry and an engineer can confirm the right Brush-block slip rings variant or an equivalent:
- Ring inner and outer diameter and stack length (mm)
- Permitted runout and axial float of the machine (mm)
- Number of circuits, current and voltage (A, V)
- Brush type and number of brushes per ring
- Speed (rpm) and expected life
- Environment inside the machine: dust, oil, humidity
- How the brush block is located and adjusted
Common mistakes to avoid
- Leaving runout and concentricity tolerances undefined between ring and brush block
- Installing rings where oil mist or swarf can reach the contacts
- Not designing an anti-rotation method for the ring assembly on its shaft
- Omitting an assembly and setting procedure for the brush preload
Fabricast Brush-block slip rings: frequently asked questions
What is the Fabricast Brush-block slip rings?
Separate rotor and brush-block slip rings with unobstructed 0.50, 1.00, 1.50 and 2.00 in through-bores for integration into the customer's own housing. Published series figures include bore 12.7 mm, bore 50.8 mm. It is made by United Equipment Accessories, Inc.; Specify Motion can help source it or propose an equivalent.
Who makes the Fabricast Brush-block slip rings?
The Fabricast Brush-block slip rings is made by Fabricast (United Equipment Accessories, Inc.) and is listed here for engineers comparing options. Specify Motion is not affiliated with United Equipment Accessories, Inc.; brand names are used only to identify the product.
What is the bore of the Fabricast Brush-block slip rings?
The published series minimum bore is 12.7 mm. Individual models and sizes in the Brush-block slip rings range vary, so check the exact variant against your duty cycle, mounting and environment, or ask our engineers to confirm the right size for you.
Is there an alternative to the Fabricast Brush-block slip rings?
Yes. On published figures, ER Series Through Bore Slip Ring and PR/PSR Series Pancake Slip Ring are the closest match from our supply network. An engineer confirms the fit against your application before recommending anything.
What is the advantage of a frameless slip ring?
A frameless slip ring removes the housing and bearings, so it is lighter, shorter and can fit large bores or tight spaces inside an existing machine. Using the machine's own bearings also avoids alignment conflicts between two bearing sets. The machine builder takes on responsibility for runout, sealing and brush setting, so it suits teams that can control those tolerances.
How accurately must a frameless slip ring be installed?
The ring and brush block must stay concentric and within the runout and axial float the supplier specifies, typically a fraction of a millimetre, so brush pressure stays even around the turn. The rings also need protecting from contamination. Ask for an installation drawing with tolerances and a setting procedure, and allow for inspection access.
Further reading: How to select a slip ring · How to specify a slip ring · Slip rings
Other open and frameless slip rings series
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