THREADED SIGHT GLASS
Threaded Sight Glass (SG-300) — NPT Sight Glass for Compact, High-Pressure Lines
When space is tight and pressure is high, the SIGHTSPEC SG-300 threaded sight glass is the compact answer. It screws directly into a tank, vessel or small-bore line with a male NPT or BSP thread, giving operators a durable borosilicate window rated up to 100 bar (1450 psi) — no flange, no clamp, no extra pipework.
PRODUCT OVERVIEW
Direct Screw-In Observation for Tanks and Small-Bore Piping
The SG-300 is the sight glass you reach for when a tri-clamp or flange simply will not fit. Its male thread installs directly into a tapped port on a tank, reservoir, accumulator or pipe — a clean, leak-resistant connection that takes minutes to fit and needs no gasket alignment. Inside, a DIN 7080 borosilicate window gives a clear view of level, color, foam, sediment and flow condition, while the compact body keeps the assembly short and unobtrusive. With 316 stainless as standard and Hastelloy or carbon steel as options, the SG-300 covers everything from hydraulic reservoirs to utility and oil & gas packages.
- ✓ Compact direct screw-in NPT / BSP mounting
- ✓ Rated up to 100 bar (1450 psi)
- ✓ Borosilicate window to DIN 7080
- ✓ 316 SS standard; Hastelloy / carbon steel options
- ✓ Thread sizes 1/4"–3" (NPT / BSP)
- ✓ Illumination, custom threads and OEM options
SPECIFICATIONS
SG-300 Technical Specifications
Standard ratings are based on published threaded sight glass practice. Confirm the final window, seal and body selection against your media, temperature and pressure before ordering.
| Parameter | Specification |
|---|---|
| Model | SG-300 |
| Mounting | Male NPT or BSP thread, direct screw-in installation |
| Thread size | 1/4"–3" (NPT / BSP) |
| Glass window | Borosilicate to DIN 7080 |
| Body material | 316 stainless steel; Hastelloy or carbon steel options |
| Max pressure | Up to 100 bar (1450 psi) |
| Max temperature | Application-dependent — confirm glass, seal and body limits with the factory datasheet |
| Sealing | Seal material selected per media and temperature |
| Options | Illumination light port, custom threads, material upgrade, OEM marking |
* Ratings are application-dependent — glass is a consumable component and should be inspected during routine maintenance. Contact the factory for the current datasheet.
CONFIGURATIONS
Three Configurations for Every Installation
All SG-300 variants share the same threaded body platform and DIN 7080 window. Choose the material and accessories that match your pressure, media and viewing conditions.
SG-300 Standard
The standard configuration: a 316 SS body with male NPT or BSP thread and a DIN 7080 borosilicate window. Sized for tight spots where a flange or clamp will not fit — tanks, accumulators, compressor packages and small-bore piping.
- •Male NPT or BSP, direct install
- •Borosilicate window to DIN 7080
- •316 SS body with seal matched to media
SG-300-L Illuminated
Adds an integrated light port so you can inspect level, sediment and condition inside unlit tanks and reservoirs. A practical upgrade for hydraulic reservoirs, lube oil systems and storage tanks where the window sits in shadow.
- •Integrated LED illumination port
- •Low-voltage operation
- •Fits all SG-300 body sizes
SG-300-C Carbon Steel High-Pressure
A carbon steel body option for utility lines, hydraulic circuits and oil & gas packages where stainless is not required and cost matters. Paired with the appropriate seal, it holds the full 100 bar (1450 psi) rating.
- •Carbon steel body for utility duty
- •Full 100 bar (1450 psi) pressure rating
- •Cost-effective for OEM quantities
APPLICATIONS
Where the SG-300 Earns Its Threads
The SG-300 is specified wherever a small, strong observation point is needed and space is at a premium. Typical installations include storage and process tanks, hydraulic and lube oil reservoirs, compressor packages, accumulators, dosing skids and small-bore utility piping. Because the window sits flush in a threaded boss, it is easy to fit, easy to swap and adds no significant pressure drop to the line.
Oil & Gas Packages
Instrument air, fuel and utility lines on compressor and process packages — see our oil & gas applications for more on how sight glasses fit these skids.
Chemical & Utility Duty
Tanks and small lines in chemical and utility plants where the carbon steel or 316 SS body matches existing piping — see chemical processing applications.
For hygienic food, beverage and pharmaceutical lines, use the SG-100 tri-clamp sight glass instead. Not sure? Send us your drawing and we will recommend the right model.
RELATED PRODUCTS
Other Sight Glass Options
Tri-Clamp Sight Glasses (SG-100)
Hygienic sanitary sight glass with zero dead-leg tri-clamp mounting.
Sight Flow Indicators (SG-200)
Flapper, rotor, drip tube and ball types for visible flow confirmation.
Flanged Sight Glasses (SG-400)
Large-window ANSI/DIN flanged units for chemical and oil & gas piping.
Browse the full range on our products overview, or read our general FAQ for ordering, lead time and documentation questions.
FAQ
Threaded Sight Glass FAQ
What is the difference between NPT and BSP threads?+
NPT (National Pipe Thread) is the US tapered pipe thread standard, while BSP (British Standard Pipe) is used widely in Europe, Asia and Australia. They are not interchangeable — the thread angles and pitches differ. The SG-300 is available with either male NPT or BSP threads in 1/4"–3"; tell us your standard and we supply the matching configuration.
How much pressure can the SG-300 handle?+
The SG-300 is rated up to 100 bar (1450 psi). The practical limit on your installation depends on the window size, body material and seal chosen — larger windows and softer seals reduce the safe working pressure. Confirm your media and operating pressure with the factory datasheet before specifying.
What glass is used, and can it take thermal shock?+
The SG-300 uses borosilicate glass to DIN 7080, which offers good thermal shock resistance compared with soda-lime glass. It is still a glass component: avoid direct cold-water spray on a hot window, and inspect it during maintenance for chips, cracks or etching.
Is the SG-300 suitable for food or pharmaceutical lines?+
The SG-300 is an industrial line sight glass built for compact, high-pressure duty — it is not a hygienic sanitary sight glass. For food, beverage, dairy and pharma piping that requires tri-clamp mounting and USP Class VI / FDA-compliant materials, use our SG-100 tri-clamp sight glasses instead.
Can you make custom thread sizes, materials or OEM versions?+
Yes. We offer custom threads, Hastelloy or carbon steel bodies, special seals and OEM-branded units. Custom projects run through our OEM/ODM process — see our OEM/ODM service page for the workflow and lead times.
Need a Compact Sight Glass Rated to 100 Bar?
Send your thread type, size, media and pressure — get the right SG-300 configuration and a factory-direct quote within 24 hours.