Yes, "Cherries / Cherry Pair" has 3.18mm connection also known as "bar". This type of connection is in system and is compatible with large variety of elements, including two you have mentioned.
Couple of examples:
The number indicates part 4719 - bicycle frame.
As you can see, it has a straight handlebars and kickstand. Your particular piece must have been modified to fit some specific purpose. Lego does not reuse the same mold numbers much, and never on the purpose, so I highly doubt if it was molded that way.
I've shuffled through my pieces collection and found sadly none in dark blue, but all 17 I've found in either old grey or red have the same attributes you mention:
Top stud is hollow, with an H-shaped cutout
There is no LEGO logo or part number anywhere
There is a small seam that runs along the full length of the part on opposite sides
There is a small ...
The piece is 72869 Bar Holder with Clip and 90° Angle (Mechanical Leg)
It's a new part for 2021, and as the name implies, one of it's main uses is as a leg on various creatures. It seems especially well-suited for building spiders:
It hasn't had many other official uses to date, but it does get used as a robot of some kind in the Marvel advent calendar:
Here are some Ideas i came up with. I added some of your suggestions for comparrison.
Mounted on top of the plate:
11458, 32013, 2780
Mounted below the plate:
32000, 32013, 2780
3701, 32013, 2780
1: two pieces from sets like 6919 - the sticker is magnetic, and fits on 30213 to make 30213pb01
2: an Insectoids torso - 973pb0037
3: an Insectoid head - 3626bpx31
4: might be a Harold Potter head - 3626bpb0155 from set 4711
5: seems to be an Insectoid helmet - 30214
The earliest LEGO bricks were made in 1949, and they had completely empty undersides with vertical notches in two of their sides for attaching windows, doors and decorative cardboard inserts:
Then in 1958 (or 1961, depending on the country) the form known today was adopted, with tubes on the bottom and without notches:
This is a torque-limiting component. When one side is prevented from turning but the other side is forced to turn, the inner piece comes out of its "click location" and into the next one.
It requires quite a large torque before it activates. You will not be able to generate the torque just by turning the two components with your bare hands. To see ...
My best guess, they are fake.
Mainly because of point 4 & 5
Lego is always very keen on hiding the seam caused by the molding
Lego include in most molds a mound number but they are always hidden out of view.
Can you read the number?
I don't have this version of the part but the other non-hollow one in white. I checked for these two marks and couldn't ...
Well, that tile wouldn't go underneath a plate. But a 2x2 round plate with rounded bottom has often been used in official sets to allow vehicles (such as boats) to easily slide over carpet, and might be just what you're looking for.
The closest I could think of in 4 x 4 size would be Turntable 4 x 4 Square Base, Locking. It doesn't feature a stud in the center and has this ring on top, unfortunately. However, depending on your use case center hole still could be used to attach whatever you are building.
The floor and ceiling aren’t one piece. They’re made of four 30357: Black Plate, Round Corner 3 x 3 each with an assortment of other square/rectangular plates to fill in the gaps.
It looks like there are 20 studs between the corner pieces on each side. The second image you posted shows a layer of tiles holding the floor together. Presumably there is another ...
Many sets have had mold changes over the years, as they get slightly redesigned, or even just wear out. I would rest at ease.
It's the old pieces that don't have ANY markings that say Lego that always worry me.
Edited: I took photos of two Duplo train track pieces I noticed today. I merged them together to show the scales are (very close to) the same, yet ...
Here are all the 4 mm diameter pneumatic tube parts Bricklink knows about.
For each of these (filtered by color if necessary) we can take the part (for example Hose, Pneumatic 4mm D. 40L / 32.0cm), check its average sale price in the "Price Guide" tab (in this case at the time of writing US $2.66), then divide that by the length to get the unit ...
I'm afraid there's no registry keeping records of elements included in each numbered part.
Instructions for 75093 set show which parts of a set could be assembled from each numbered bag, including parts for each step. You can then collect elements listed under each step to combine into numbered bags of your own. Getting all extra pieces might be a little ...
Step 45 of instructions for 42100 set shows entire drive-train for one side of the tracks before it is being covered with some panels and beams. I've taken that image and have drafted a rough path between the motor and Tread Sprocket Wheel that will then transfer this motion to tread links.
As you can see Clutch is within this drive-train, so it makes clear ...
This motor was not easy to take apart. Unlike some of the others that have screws or clips that can be released, I wasn't able to get into this one without basically cutting it in half. If you need to repair one of these, it is possible to get it apart and put it back together, but I believe that glue would need to be involved to hold it securely together ...
I do not own this item, but observing the pictures leads to a logical inference.
The pins are in different locations.
If you look at parts, you will see that they are 5 pins wide. One part has pins in positions 1 and 5, the other has pins in positions 2 and 3.
You then connect the parts to the motor. With switches inside the motor, it can detect which ...
Any metallic or metal coated parts (spoon, aluminium foil, pen) should be usable with a contemporary touchscreen, although proper touch recognition still requires a human (or an equivalent capacitor) to touch the conductive surface. Therefore theoretically any of these official LEGO parts with exposed metallic surfaces (or similar ones) should function, ...
According to SylvainLS in this BrickLink post, these are the answers to my questions:
You can find out which colors are available for a part by selecting a part, opening the Color Palette on the right side of the interface, and selecting the Hide unavailable colors option.
In the BrickLink catalog, part 99455 and many other EV3-specific pieces are set to ...