Product Overview
Swagelok B-600-6-4: The Brass Union That Takes 3/8 in. Tube Down to 1/4 in.
Condition
Unused new old stock. The photo shows several brass fittings bagged together in a clear poly bag, and the piece you receive is representative of that stock; our shelf count for this part number is two. What the camera can actually read on the brass is partial: a 3/8 on one nut flat and the tail of a Swagelok engraving on a body. The full B-600-6-4 designation comes from our catalogue record, not from a reading of the part, so if you need the number verified on the metal in hand, ask before ordering. The brass carries the ordinary bright-and-dull mix of stock that has sat on a shelf, with no visible thread damage or flat rounding.
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Product Overview
A reducing union is the plainest answer to a common plumbing problem: a run of 3/8 in. OD tube has to become a run of 1/4 in. OD tube, and nothing threaded or soldered belongs in between. Swagelok publishes B-600-6-4 as a current catalogue item, a brass Swagelok tube fitting, reducing union, 3/8 in. x 1/4 in. tube OD, with a gaugeable two-ferrule compression end on each side. Each end takes the tube directly under a nut with a front and back ferrule behind it, so the joint is made by pulling the nut up rather than by cutting threads into the tube or heating anything. The catalogue lists it as not bored through and carrying no flow restrictor, with an overall length of 1.70 in. per the reducing union table in Swagelok's MS-01-140 catalogue. Swagelok's brass fitting components are specified to ASTM B16 and B453 for bar stock and ASTM B283 for forgings, a series-level material statement rather than a certificate for this individual piece, and the catalogue page lists the part under Standard Cleaning and Packaging, SC-10. This listing gives no pressure number, on purpose. Swagelok rates tube fitting ends to the working pressure of the tubing they are installed on, per Swagelok Tubing Data MS-01-107, and that document carries no brass tubing table, so no psig figure honestly describes this fitting. The 3,900 and 2,600 psig figures floating around the brass literature are pipe thread ratings for NPT and ISO ends, which this union does not have on either side.
Key Features
- Swagelok B-600-6-4, brass Swagelok tube fitting, reducing union, current catalogue part number
- Joins 3/8 in. OD tube to 1/4 in. OD tube, end to end
- Gaugeable two-ferrule Swagelok compression end on both sides: nut, front ferrule, back ferrule
- Brass body; Swagelok specifies ASTM B16 and B453 bar stock and ASTM B283 forgings for its brass fitting components
- Overall length 1.70 in. per the Swagelok MS-01-140 reducing union table
- Not bored through, no flow restrictor, per the Swagelok catalogue listing
- Listed by Swagelok under Standard Cleaning and Packaging, SC-10
- Condition: unused NOS; sold each, two on the shelf
Applications
- An instrument tech bringing a 1/4 in. sample line into a 3/8 in. header on an analyzer panel without adding a threaded joint
- A lab building a bench gas manifold where the regulator outlet and the apparatus inlet were never the same tube size
- A maintenance shop repairing a pneumatic run and finding that the original fitter changed sizes mid-line
- A process skid builder keeping one brass transition in the spares drawer so a size mismatch never stops a Friday tie-in
Frequently Asked Questions
What exactly does this fitting connect?
3/8 in. OD tube on one end and 1/4 in. OD tube on the other. Both ends are gaugeable Swagelok two-ferrule compression ends, so the tube goes in bare and the nut does the work. There is no pipe thread, no flare and no solder joint anywhere on this part.
What is it rated for?
Swagelok does not publish a pressure rating for a tube-to-tube fitting like this one. Its own rule is that Swagelok tube fitting ends are rated to the working pressure of the tubing they are installed on, as listed in Swagelok Tubing Data MS-01-107, which means the rating follows your tube OD, wall thickness and temperature rather than the union. MS-01-107 carries no brass tubing table, so we publish no psig number and no temperature range for this fitting. Not confirmed - verify against the datasheet before use.
How big is it?
The Swagelok catalogue table MS-01-140 gives an overall length of 1.70 in. for B-600-6-4. We are quoting the catalogue figure rather than a tape measure reading off the photo, because the fitting was photographed bagged and a ruler read through poly is not a measurement.
Can you confirm the part number off the part itself?
Only partly, and we would rather say so. The photos show a 3/8 on a nut flat and a partial Swagelok engraving on a body; the complete B-600-6-4 string is not legible in the frame. The part number on this listing is the one our catalogue record carries for this stock. Swagelok's own grammar backs it up: B is brass, 600 is the 3/8 in. body size, and the trailing 6 and 4 are the two tube sizes in sixteenths.
Why buy this one fitting instead of a surplus box of mixed brass?
Because you can see what you are getting before you spend anything. This is a single catalogued size combination, unused, photographed on our bench, and sold each out of a shelf count of two. A mixed lot is cheaper per piece and useless at 4 p.m. when the one transition you need is the one that is not in it. Shipping is a flat $8 per order, free once the order passes $28, and orders leave our Idaho warehouse the same or next business day.
Swagelok part numbers are a small private language: B for brass, 600 for the body, and the trailing 6 and 4 counting sixteenths of an inch at each end. Somewhere in your line two tube sizes have to come to an agreement, and this is the piece that negotiates it.
