--- title: "What Are Hydraulic Compression Fittings Used For?" description: "Hydraulic Compression Fittings (DIN 2353) are used for joining and sealing fluid or pneumatic lines. Catalogued 4 to 42." url: https://engineeringhardware.com/applications/hydraulic-compression-fittings/ source: Engineering Hardware & Fasteners --- # What Are Hydraulic Compression Fittings Used For? Pipe & Pneumatic Fittings · DIN 2353 · Application guide Typical applications, the industries that specify hydraulic compression fittings, and how to choose the right size, material and finish for the joint. Hydraulic Compression Fittings are used for joining and sealing fluid or pneumatic lines. They are manufactured to DIN 2353, and selection is driven by the pipe thread size, the fit and tolerance the assembly requires, and the service environment. - **Primary duty:** Joining and sealing fluid or pneumatic lines - **Governing standard:** DIN 2353 - **Pipe thread size range:** 4 to 42 - **Category:** Pipe & Pneumatic Fittings Application notes are general engineering guidance. Verify the property class and any approval requirement against your own design calculation. ![What Are Hydraulic Compression Fittings Used For? application image](https://engineeringhardware.com/wp-content/uploads/2026/06/Hydraulic-Compression-Fittings-—-DIN-2353.webp) Hydraulic Compression Fittings are used primarily for joining and sealing fluid or pneumatic lines. This page lists the industries and assemblies where they are specified, the selection criteria that matter for each application, installation practice, and the cases where a different fastener type is the correct choice. Parts are supplied to DIN 2353. Stocked across roughly 4 to 42, they cover general to heavy-duty work. ## Typical Applications for Hydraulic Compression Fittings The most common settings where these are specified: - **General machine building:** fastening covers, brackets, motors and sub-assemblies on production equipment. - **Maintenance & repair (MRO):** a stocked size for servicing existing plant where the original fastener spec must be matched. - **Fabrication & metalwork:** bench and on-site assembly of steel frames, enclosures and weldments. - **Pneumatic systems:** connecting air lines, cylinders and valves on automation rigs. - **Hydraulic & fluid power:** sealed, pressure-rated joints in fluid lines. ## How to Specify Hydraulic Compression Fittings for Your Application - **Size:** Match the nominal size to the mating thread or hole. This product spans 4–42; check the full table below for the exact dimensions of each size. - **Thread & pressure:** Match the thread form (BSP/NPT/metric) and pressure rating to the line, and seal appropriately (tape, sealant or O-ring). - **Environment:** For damp, coastal or chemical exposure prefer A4/316 stainless or a suitable coating; indoors, plated steel or A2 is usually sufficient. - **Standard:** This product is supplied to DIN 2353. Quoting the standard on your order guarantees interchangeable dimensions between suppliers. ## Installation & Assembly Practice - Seal tapered threads with PTFE tape or anaerobic sealant applied clear of the first thread; parallel threads seal on a washer or O-ring, not on the thread. - Tighten to the fitting manufacturer's torque — over-tightening tapered threads splits female ports. ## Common Selection Mistakes with Hydraulic Compression Fittings - Mating BSP and NPT threads directly — the 55°/60° forms do not seal against each other. - Exceeding the pressure rating of the lowest-rated component in the line. ## Where Hydraulic Compression Fittings Are Not the Right Choice Do not mix thread forms (BSP into NPT) without an adapter, and do not exceed the pressure rating of the lowest-rated component. Custom manufacturing · Made to drawing ## Need a hydraulic compression fittings outside the standard range? Dimensions, material, finish and form are specified from the drawing — a pipe & pneumatic fitting outside the standard range is a variation on existing tooling rather than a new design. Minimum order from 2,000 pieces; samples within 7 days of drawing approval. [Custom pipe & pneumatic fitting manufacturing](https://engineeringhardware.com/custom/fittings/)[Send a drawing](https://engineeringhardware.com/custom/fittings/#rfq) ## Technical Drawing Dimensioned line drawing of 4 Hydraulic Compression Fittings to DIN 2353. Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected. - **Nut length L (mm):** 22 - **Nut width across flats (mm):** 13 - **Tube bore (mm):** 8 - **Max working pressure (bar):** 400 - **Mating thread:** M10x1 - **Notes:** Compression hydraulic fitting ## Dimensions & Specifications (DIN 2353) | Tube OD (mm) | Nut length L (mm) | Nut width across flats (mm) | Tube bore (mm) | Max working pressure (bar) | Mating thread | Reference standard | Notes | | --- | --- | --- | --- | --- | --- | --- | --- | | 4 | 22 | 13 | 8 | 400 | M10x1 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 5 | 24 | 14 | 9 | 400 | M12x1.5 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 6 | 27 | 17 | 11 | 400 | M14x1.5 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 8 | 30 | 19 | 13 | 400 | M16x1.5 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 10 | 33 | 22 | 16 | 400 | M18x1.5 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 12 | 36 | 24 | 18 | 315 | M22x1.5 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 14 | 39 | 27 | 20 | 315 | M26x1.5 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 15 | 39 | 27 | 20 | 315 | M26x1.5 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 16 | 42 | 30 | 22 | 315 | M26x1.5 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 18 | 45 | 32 | 25 | 250 | M30x2 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 20 | 48 | 36 | 27 | 250 | M30x2 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 22 | 51 | 38 | 30 | 250 | M36x2 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 25 | 55 | 41 | 32 | 250 | M36x2 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 28 | 58 | 46 | 36 | 160 | M42x2 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 30 | 60 | 48 | 38 | 160 | M42x2 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 35 | 66 | 55 | 44 | 160 | M52x2 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 38 | 69 | 58 | 47 | 160 | M52x2 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | | 42 | 74 | 65 | 52 | 100 | M60x2 | DIN 2353 / ISO 8434-1 | Compression hydraulic fitting | Inside the plant ## Manufactured in our own plant This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided. 1. ![Wire rod feeding into a cold heading machine](https://engineeringhardware.com/wp-content/uploads/2026/08/09-wire-rod-feed-cold-heading-machine.webp) 01 **Cold heading** Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail. Head dimensions and under-head radius checked at set-up and per shift. 2. ![Thread rolling machine producing bolt threads](https://engineeringhardware.com/wp-content/uploads/2026/08/03-thread-rolling-machine-bolt-production.webp) 02 **Thread rolling** Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch. Go / no-go ring gauges to ISO 965 tolerance class 6g. 3. ![Baskets of bolts staged for heat treatment](https://engineeringhardware.com/wp-content/uploads/2026/08/05-heat-treatment-baskets-black-bolts.webp) 03 **Heat treatment** Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it. Core hardness and tensile tested per lot to ISO 898-1. 4. ![Zinc plated bolts in a treatment basket](https://engineeringhardware.com/wp-content/uploads/2026/08/23-zinc-plated-bolts-treatment-basket.webp) 04 **Surface treatment** Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list. Coating thickness and neutral salt spray hours to ISO 9227. ## Frequently Asked Questions ### What are Hydraulic Compression Fittings used for? Joining and sealing fluid or pneumatic lines. They are supplied to DIN 2353. ### Which industries use Hydraulic Compression Fittings? They are commonly specified in fabrication & metalwork, pneumatic systems and hydraulic & fluid power, among other sectors. ### How do I choose the right size of Hydraulic Compression Fittings? Match the nominal size to the mating thread or hole. This product is available from 4 to 42; the full dimension table on this page lists each size. ### Can I mix BSP and NPT Hydraulic Compression Fittings? Not directly — the thread forms differ in angle and taper. Use a dedicated BSP-to-NPT adapter, and seal with the method suited to the thread (tape, sealant or O-ring). ### Can I get a quote for Hydraulic Compression Fittings in the size and material I need? Yes. Use the technical drawing and quote form on this page to set the size and options, then send the exact configuration to our team for pricing and lead time. ## Related Pages Product page: [Hydraulic Compression Fittings — specifications & sizes](https://engineeringhardware.com/fastener/hydraulic-compression-fittings/) ### Hydraulic Compression Fittings Specification Guides ### Related Fastener Applications