4–1 Merge & Slip-Fit Jig

Merge and parallel slip-fit collector fixtures for thin-wall tube. Eleven configurations covering 1.50" through 2.50" OD primaries in 16 and 18 gauge — the material most stainless headers are actually built from, and the one where a bad tack warps the throat.

There is nothing else like this, printed or machined. Merge collector fixtures are not something you can go and buy — which is why most people tack four tubes by eye and find out it is wrong after the weld cools. The thing this saves you is not a tool purchase; it is the collector itself, plus the hours in it.

What you download

• STL file for the configuration you choose
• Merge collectors: 1.50" OD 5.00" tall / 2.50" round · 1.75" OD 3.00" tall / 2.00" round · 1.75" OD 5.00" tall / 2.50" round · 1.88" OD 3.00" tall / 3.00" round · 2.00" OD 3.00" or 5.00" tall / 2.50" round · 2.00" OD 3.00" tall / 3.50" round · 2.25" OD 3.00" tall / 4.00" round · 2.50" OD 3.00" tall / 5.00" round
• Parallel single slip-fit: 2.00" OD → 2.00" out · 2.25" OD → 2.25" out
• Instant download at checkout. Nothing ships.

Why slip-fit

A parallel slip joint comes apart. On a race car that means you pull a section for repair without cutting welds, and the joint absorbs vibration instead of cracking. On a street build it means you can actually get the thing back out of the chassis.

Print settings

My official settings for every G1Pro fixture: 2.5 mm walls, 2.5 mm top and bottom, 20% cubic infill, support-free, printed in Inland PETG-CF.

Licence — Shop Use

Print as many copies as you like for use in your own shop, including on paying customer jobs. You may not share or resell the file, or print copies of the fixture to sell. Print-and-sell licences available — ask.

Drawn by James Goertz, G1Pro. Building intake manifolds by hand since 2009; these are the fixtures off my own bench.