This is a74mm model rocket body tube adapter.

It connects 2 (74mm) x cardboard body tubes.

It is designed to be used with body tubes like this ones:
Apogee - 74mm x 18" Body Tube (Thin Wall 3" tube)

It is meant to substitute 3" Tube couplers, such as:
Apogee - Tube Coupler for 3" diameter Thin-Wall Model Rocket Body Tubes

The printed part, weights less than the cardboard couplers by a few grams.

You will need 4 screws (2.5/3mm) to hold the coupler to the tube in place.

CAD Fusion360 model included in files

Print instructions

Category: Vehicles Print Settings

Printer Brand: Prusa

Printer: I3 MK3S

Rafts: No

Supports: No

Resolution: 0.2

Infill: 10

Filament: ANY PLA - PETG
Notes:

Print this with the rounded part facing down.
Does not need support at all.