Housing body material
Start with the installation conditions
Bently Nevada 21000 and 24701 Proximity Probe Housing Assemblies solve the same mounting problem, but they are not selected by series name alone. Begin with the machine environment and required housing material, then confirm the probe family, sleeve geometry, conduit fittings and approval as one coordinated configuration.
The first decision is the body material. Choose the 21000 when the documented installation calls for an aluminum housing; choose the 24701 when it calls for a 303 stainless-steel housing. Both use a 304 stainless-steel sleeve, so this choice changes the housing body and mass rather than the basic external-probe mounting function.
After the body is selected, match the reverse-mount probe and its transducer system. Ordering options cover 3300 XL 8 mm, 3300 XL NSv and 3300 XL 11 mm probes. The sleeve, cable lead, standoff, penetration, fittings and mounting thread must then describe the actual distance from the machine mounting surface to the target.
Four decisions determine the housing
- Material: aluminum 21000 or stainless-steel 24701 body.
- Probe system: the exact reverse-mount probe and approval option.
- Geometry: sleeve, standoff and penetration dimensions.
- Installation boundary: fittings, mounting thread and hazardous-area approval.
Choose 21000 or 24701 by body material
| Engineering item | 21000 housing | 24701 housing |
|---|---|---|
| Body material | Aluminum | 303 stainless steel |
| Sleeve material | 304 stainless steel | 304 stainless steel |
| Typical mass, without fittings | 1.1 kg (2.4 lb) | 1.8 kg (4.1 lb) |
| Housing width A | 83.3 mm (3.28 in) | 78.2 mm (3.08 in) |
| Housing height B | 161.6 mm (6.36 in) | 151.9 mm (5.97 in) |
| Lower housing dimension E | 26.7 mm (1.05 in) | 27.9 mm (1.10 in) |
| Probe families available through ordering options | 3300 XL 8 mm, 3300 XL NSv, 3300 XL 11 mm and selected legacy or special probe options | |
| Certified enclosure / installation context | CA21000 and CA24701 versions: CSA Type 4 and explosion-proof approvals for specified North American hazardous areas; standard 21000 and 24701 versions are used for other end-user countries | |
Dimensions C and D are configuration-dependent. Use the selected standoff-adapter and probe-penetration codes rather than assuming a fixed overall sleeve length.
Match every mechanical part to the selected housing
Once the 21000 or 24701 body is chosen, the remaining parts must reproduce the real machine geometry. Each component controls a different boundary, so a housing body cannot be selected independently from the probe, sleeve, standoff, fittings and mounting thread.
Compare only the details that differ
The shared sleeve, threaded connection and probe protector are intentionally omitted. The views below focus only on the housing-body differences that separate the 21000 from the 24701. Click any detail to open the complete high-resolution original.
Difference 1 — housing body material and proportions
Not shown because they are not the differentiators: both families use a 304 stainless-steel sleeve and can share the same probe-family, fitting and mounting-thread choices when those order-code fields match.
Verify the housing and sleeve geometry
Translate the installation into the order code
The 21000 and 24701 records use the structure 21000-AA-BB-CC-DDD-EE-FF or 24701-AA-BB-CC-DDD-EE-FF. The complete string matters because it defines the probe and the mechanical installation together.
Choose the reverse-mount probe family, connector-protector execution and approval option that matches the associated transducer system. If no probe is supplied, use the documented no-probe option rather than inferring a probe from the housing.
Available probe-lead selections include specified imperial and metric lengths. The probe lead must be longer than the sleeve, and the cable option must remain consistent with the probe system.
Option C defines the optional standoff adapter; option D defines probe penetration. C is ordered in 0.5 in increments and D in 0.1 in increments within the published limits.
Options cover no fittings, explosion-proof fittings, plugs, reducers and cable-seal grips. The fitting selection must match the conduit and approval arrangement.
The final field identifies the mounting thread. Verify the machine-side tapped opening and the required thread engagement before the sleeve length is finalized.
Keep the housing, probe, sleeve, standoff, fittings and mounting thread together in the purchasing and installation record so field geometry remains traceable.
Prevent selection errors during installation
Support long sleeves before resonance becomes a problem
If the combined sleeve arrangement extends beyond 304 mm (12 in), add support near the probe. Bently Nevada identifies probe support and oil seal part number 37948-01 for long sleeves that pass through an inner bearing housing, and custom supports may be required for other machine geometries.
Keep the probe lead longer than the sleeve
The cable must reach through the housing without being tensioned by the sleeve arrangement. Select the lead length after the mechanical C and D dimensions have been established, not before.
Set probe position with the matching probe-system procedure
Mounting the housing does not replace the probe-system setup. Gap, target material, extension cable and Proximitor sensor still belong to the selected 3300 XL or NSv system and must follow that system's installation limits.
Do not infer hazardous-area approval from a fitting alone
Explosion-proof fittings are available for multiple configurations, but only the specified CA housing versions carry the stated CSA explosion-proof housing certification. Confirm the entire ordered assembly and the applicable country approval before installation.
Confirm hazardous-area approval before ordering
CA21000 and CA24701 housings are certified for specified Class I, II and III North American locations. Temperature-code limits and drawing requirements still apply to the completed installation.
The 21000 and 24701 housing families are designed around the externally mounted proximity-probe housing requirements referenced by API 670, including accessible probe mounting and defined mechanical support.
Selection questions before requesting a quotation
When should I choose the Bently Nevada 21000 instead of the 24701?
Can a 21000 or 24701 housing be ordered without a probe?
Why does the 21000 or 24701 sleeve need extra support?
Does an explosion-proof fitting make every 21000 or 24701 housing explosion proof?
Can the 21000 and 24701 use the same probe families?
How do I determine the C and D dimensions for a 21000 or 24701 housing?
Why must the probe lead be longer than the 21000 or 24701 sleeve?
What information should I send when requesting a 21000 or 24701 quotation?
Recommended products
Mixed-brand catalogue references for proximity measurement, vibration monitoring, signal conditioning and industrial control. They are product suggestions for separate review, not claims of direct interchangeability with a 21000 or 24701 housing.
Send the complete configuration
Include the housing model, quantity and installation details so the selection can be checked before quotation.