Coupling · clear · 2-1/2 in
POWERTEC 70234-P2 pipe coupling, 2-1/2 in, 2 pack
The only transparent fitting on this shelf — which on the diameter that blocks most often is the specification that counts.
Every figure below names its source. Each one is a manufacturer
specification read off the listing itself. The judgments are ours.
Clear
The only transparent fitting on either half of this shelf, and the reason to buy
it.
Blockages form at joints. A step in diameter, a ridge of adhesive, a square
shoulder — the first long shaving catches, and everything behind it packs.
In opaque duct that is found by tapping along the run. In a clear coupling it is
seen.
Two published pages on this shelf make the identical argument about hose, and
both are transparent for it. This is the only fitting that is.
Two point four nine, tapered
An inner diameter that opens at 2.49 in and narrows, against an outer of 2.74.
A parallel bore either slides on loose or jams in the first inch. A tapered one
grips progressively, so the pipe seats and stays.
The listing calls it an airtight friction fit. It is a friction fit, and on a
duct that will be there in a year, tape or a clamp over the joint is what keeps
it airtight through the vibration.
Why nominal is not a measurement
A four-inch fitting is not four inches anywhere on it.
The POWERTEC listings on this shelf publish the actual figures: a four-inch
nominal end measures 3-31/32 in across the outside and 3-39/64 in across the
inside — 100.8 mm (3.97 in) and 91.7 mm (3.61 in). The difference between those two is the wall, and
the difference between one maker’s outside and another’s inside is the leak.
That is what the shelf’s own intro means by the adaptors that never quite fit.
Nominal sizing is a naming convention; the join is decided by the sixty-fourths.
Not a machine size.
A table saw or a planer port wants four inches, and 2-1/2 in front of it starves
the machine — the extraction pages in this catalog are full of that arithmetic.
What 2-1/2 is for: a random orbital sander, a track saw, a biscuit joiner, a
router. It is also the diameter a shop vacuum hose actually is, which is why the
Rockler adapter set on this shelf steps down to it and below.
Availability
Read on the day this page was built: $20 at the American Amazon shop.
Read from Keepa on the day this page was last revised; stock and price both move without notice.
Prices quoted in this text were read on 2026-10-07. The live price is at the top of the page.
