This design is a modular system to hold things securely. I designed it to use in electrochemical experiments and it is inspired by lab stands (statifs). It is also helpful for soldering or any cases you would use a 3rd hand. You may watch this video for a quick introduction to this system: https://youtu.be/XsCk5LUepSI

This system is designed primarily to be very stiff, versatile and cheap. I designed it around 4 main types of elements:

Base plates to provide stability and strong attach points
8 mm bars
Connectors to rigidly assemble the bars
Clips of different types to hold any object you are working with
For some applications it is possible to use 3D printed bars, however i prefer to use 8mm stainless tubes with 6mm inner diameter (1mm walls). Such tubes provide an excellent balance between high stiffness, medium weight, medium cost and excellent durability. I have prepared a variety of sizes and it works well for kg range loads on up to 40cm long tubes.

Besides the tubes, this system relies on M4 bolts and melt inserts. The bolts should be 10 mm long internal hex and the melt inserts should be 5 mm long and designed for 5 mm holes.

On this page you will find all the essential elements to make your own holder kit. Here is a basic description of the parts and how they are named:

Bar_dimentions are simple bar models with different sizes. you can print those with strong parameters (5 walls or more) if you do not want to use 8mm metal tubes.
Bar_T_dimention are bars of various sizes with an attachment point for other bars at the extremity
T_extension are attachment point extensions for metal tubes. It is sometimes useful as it is more compact than using 90d connectors
Base_plate_shape_dimention are the various base plate available described by their dimensions. Each base plate should be printed with as many knobs as they have attach points
Connector_angle_particularity are connectors to attach tube elements together at the specified angle. each connector should be printed with two knob (3 for the "90d_3_bars") . The "8_to_10mm_axes" connector can be used with axes as large as 10mm and is compatible with many standard lab stands.
Optical_table_rod_holder are designed to fix 8 mm rods on optical tables with standard M6 or 1/4"-20 threaded hole arrays. each one should be printed together with 1 knob
Clip_M3 are basic printed clip elements using one 20 to 25mm M3 screw
Clip_aligator_metal are holders for metal alligator clips with 4mm female connectors (banana clips). Such clips are inexpensive and can be found on your favorite website. Just make sure to take ones with 4mm tube bases. The holders are designed to hold the clip by friction and ensure a good hold while allowing rotation.
Organizer is a large organizer to fit various base plates, connectors and tubes
Rack_dimention are holder with holes to keep tubes and any other elements with 8 mm bars
For the sake of simplicity this page only contains the fundamental elements of this holder system. More specialized elements, useful but less versatile, are posted bellow:

Printed clips with clothespins' springs: https://www.***********.com/thing:7336779
Precision translation system: https://www.***********.com/thing:7334794
Specialized holders (flashlights, digital microscope): To be released shortly
This holder system relies on M4 screws to allow quick and rigid adjustments and knurled knobs to give you a good grip. If you want larger or thinner knobs (for better grip or more compacity) you can find it here: https://www.***********.com/thing:7316340
If you build a lot of those elements you will also find there some protections to print in TPU and use to grip the knobs with pliers when fixing the M4 bolts inside.

Modular holder system (3rd hand / lab stand)

0.2mm layer, 4 walls, 25% infill

0.2mm layer, 2 walls, 15% infill