The presentation that senior Lego designer Jamie Berard held at Brickcon 2006 and that spawned the entire legal vs illegal discussion can be found here:
The particular case you ask for is discussed in slides 9 and 10:
A 1x1 cone with an inverted positioned screwdriver just might work here.
So, I'm saying just might based off the the halved cast line of Peggy's head.
The base peg of the horn/drill-bit would be too wide for the hole, but based off the cast fault line, which I hi-lighted in blue, there is a greater chance for the plastic halves to ease the slimmer screw ...
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:
Put two plates between each layer of Technic bricks and the holes will align.
This technique was used commonly in studded Technic sets. Here's a page from the instructions for 8042 where you can see this used in several different places:
If the problem is that the base of the horn is too big to fit in the hole on the chanfron you have to make the former smaller or the latter bigger. Careful work with a file/scalpel, if you're good at that kind of thing. Remember that it's a lot easier to take a bit more off than to put a bit back.
Odd that the bow doesn't use a standard size stud anyway (...
A possibility might be using Horse Battle Helmet (unicorn) parts 89524 or 13745:
However I'm unsure if those would fit. The head geometry of the horse part in question (93083c01pb08) seems to be wider than the geometry of the horses in the castle sets (e.g. 10352c01pb03)
If you're not afraid to modify (cut and/or bend) one of the horse helmets, they might ...
According to LEGO, this type of connection is illegal, since the pin is stressed when connected to an anti-stud and eventually deforms.
People's MOCs do not follow same policy as TLG does. So you may encounter illegal connections from time to time. Pins are also cheap and usually owned in high numbers, so nobody's really bothered if one gets deformed.
In general, this sort of connection is illegal, but I think that it works fine with a Travis brick. Technic pins must be "in click" in a model, or the pins will be held in compression and can be damaged over time.
Here's a slide from Jamie Barard's classic "Stressing the Elements" presentation that explain the need to have Technic pins in click:
And here's ...
I suggest using 4175 1x2 plate with ladder together with 3839 1x2 plate with handles SNOTted together with the help of 4070 1x1 brick with headlight, one 2x2 plate and 2 1x2 plates, like so:
Yes, the whole thing is upside-down. This is normal.
This contraption will hold the 2x3 tile snugly, thanks to the offset provided by the lip of the headlight brick. ...
I don't have this particular piece but my advice for most 'non-standard' connections such as these is to use a part that is flexible enough to fit the gap.
The 'Technic, Axle Connector Double Flexible' piece under compression can make a snug enough fit to mount a sharks head.
In this example, you can use two Technic Axle-Pin attached to another two ...
this way it can open and close
Blue = 4276 Hinge Plate 1 x 2 with 2 Fingers
Yellow = 4275 Hinge Plate 1 x 2 with 3 Fingers
LightBlue = Plate 2 x 4
White = Plate 2 x 2
Pink = Plate 1 x 4
Light Bluish Gray = Plate 1 x 3
Yellowish Green = Plate 1 x 2
Red = Tile 2 x 2
Green = Tile 1 x 4
I don't think there are any pieces LEGO intends for you to attach to the side of these axle shaped pieces. However, I'm pretty sure you could attach piece 32172 to some extent (assuming the piece being attached to is actually the right size for an axle):
It probably would not connect very well, only the clips on the sides of the socket would hold it, so it ...
Okay, it seems I indeed made a mistake during building, which I solved afterwards:
When assembling the rear mudguard, I noticed that the rear wheel had quite a bit more variability in its sideways adjustment and was quite a bit off center, specifically too far to the left. This caused the chain belt to either run slightly skewed or have friction on some ...
Yes, you can drill it. Slowly, by hand. You want to end up with a 1/8 inch bit, but I found it easier to step up using a couple of smaller bits to get there. The bit doesn’t need to go in very far when you’re drilling.
It’s certainly not for purists, but it suits my kids just fine 😊
There is a bit of a challenge with a geometry. LEGO doesn't produce much symmetrical hinges, otherwise they would be out of system. I could think of the following one piece you could achieve a close result - Hinge Plate 2 x 4 with Pin Hole and 3 Holes - Top. It comes in White color as well, so you could incorporate in your layer of white plates.
Here's a ...
Scientific progress goes OINK!
This is an older DUPLO pig from the 70's, and its different design offers us some new possibilities.
For example there's a rectangular hole below the neck.
Now before we go any further, the LEGO policeman would like to remind everybody that stuffing plates into rectangular holes or jamming them between studs isn't exactly ...
I am still waiting for the bricklink delivery with 27448 tiles that Alex suggested in one comment of his answer. Therefore, I tried a less subtle solution:
This is the starting point: A DUPLO pig that needs to be put directly on LEGO pieces.
I decided to cut a DUPLO piece to regular LEGO size. A DUPLO 2x2 brick was converted to a ...
... 4x4 tile, ...
Although technically the connection is illegal, I don't think the pin is under stress. I remember this set from my childhood, and the "rotor" rotated easily, which would not have been the case if the pin was stressed.
Is there a good way to attach it to common plant stems (3741)?
Although strictly a non-official connection, the Technic pneumatic hose (or its rigid variant) can fit over the plant stem, and thus the Friends flower pin. If the connecting piece is cut short enough, the resulting assembly might even look somewhat good.
Have you tried horizontal clips? They will be a little taller than 1 plate in the center, but you might be able to adapt them to your needs given that the connection point is just one plate. Perhaps these parts:
Something like 4623 with a vertical clip might also be a possibility depending on your constraints:
Mr. Blue and Ms. Red live next doors. Their houses are simple. The walls are one stud wide, the ceiling's one plate thick, some slopes on the roof.
Now they want to move their houses wall to wall. Mr. Blue bores a hole into the wall and happily bolts in a big peg. But Ms. Red thinks that's just a big eyesore!
So they try to hide some clips in the ceiling, ...
I'm gonna suggest a different, non-conventional approach. This revolves around offsetting some 6016 3x4 grille, so each 2x3 tile fits through several grilles at once:
For an even more minimalistic look, rely on 4733 1x1 brick with studs on 4 sides and 2555 1x1 tile with clip, then add your own 1x1 brick/plate column:
Given the difficulties of making this ...
What does 18853 (Friends flower) connect to?
Most of Friends animals have this type of connection to attach accessories like flower you mention, bow or other. Coule of examples:
Dolphin, Friends / Elves, Jumping with Bottom Axle Holder with Medium Azure Eyes with Eyelashes Pattern
Bear, Friends / Elves, Baby Cub, Sitting with Black Nose and Claws and Dark ...
I'm very late to the game here, but why can't we use the existing hole as a guide for an appropriately sized drill bit, converting it from Friends accessory size to standard LEGO horn size? If you drilled it slowly by hand, it would be really hard to mess it up.
It doesn't look like there's currently any way to make this connection by normal means.
While there are quite a few parts with similar 1.6 mm attachment holes as your daughter's horse has (including some mildly surprising ones like this ladybug), parts with the matching pins seem to be relatively few. Basically all of them seem to be small ornaments like ...