Each of these 4 LED-holders can hold four 5mm LED's and one 3mm LED (in the center hole).

They were designed to fit inside a "Red Bull Energy Shot" PET bottle cap and "hide" within the cap so that it doesn't come down below the edge of the cap.
They should fit into any bottle/tube that has an inner diameter of 25mm inner diameter and an outer diameter of approximately 29mm.

There is approximately 7mm clearance between the top of the bottom plate and the top of the ring.
This should make loads of room for resistors and/or LED-driver circuitry.

The LED holes were designed with an diameter of 5.0mm and the "safety springs" have a diameter of approximately 4.9mm in relaxed state.
I have noticed that some LED-manufacturers have a +- 0.25mm tolerance on their LEDs.
I will try these LED-holder and update the model with more clearance if that seems necessary.

I have bundled 4 LED holders into the model because if they were ordered one by one the startup cost would be more than the actual material cost with certain materials.

Some materials are restricted due to wallthickness and the need for atleast some degree of flexibility in the "springs". Alumide might be too stiff and fragile but I'll leave it up to you to decide.