I'm going to write about front single-speed chainring bolts.
The image above shows front single-speed chainring bolts from the same manufacturer, but
these are different parts with different part numbers.
One is for single-speed with the cylindrical portion on the nut side measuring 4.5mm,
while the other one just says "for single-speed."
↑The image on the left is 4.5mm,
and the nut on the right is longer than that, so if we call the left one 4.5mm, this one would be 6.5mm.
The bolt side is also different—
the 6.5mm one has a longer threaded section,
and there's a faint unthreaded zone at the base.
Looking at the Wolf Tooth (ウルフトゥース) chainring,
among my collection of 34T, 36T, 44T, 46T, and 48T rings,
from 46T onward the outer holes on the chainring become counterbored—that is, they have a flush-fit design.
It seems Wolf Tooth's assumption is that you'd mount to the outer chainring position starting from 46T.
Update: I received a comment that there are also 38T rings for 4-arm cranks with counterbored holes.
The counterbore cutoff might vary depending on PCD and intended use (road, MTB, or cyclocross).
Thanks for the comment.
The back side doesn't have counterbored holes.
The chainring bolt sits flush in the counterbored hole.
So the bolt head and chainring are roughly flush with each other.
But with 44T and below (the image shows 36T),
the outer side doesn't have counterbored holes, and
neither does the back side.
Yet Wolf Tooth chainrings are unusually thick, so the shorter chainring bolts (the 4.5mm ones mentioned earlier) aren't long enough to use. So what do you do?
You have to mix and match—use a double-speed nut and single-speed bolt, for instance.
The reverse won't work (I'll explain later).
Here's my bike in the 4kg range.
Currently it has a Rotor (ロター) oval chainring on it.
I don't have strong opinions about ovals, so I could switch to Wolf Tooth, but...
If I went with Wolf Tooth, I could also remove this chain watcher.
As I mentioned before,
Wolf Tooth chainrings are unusually thick, so they're not light.
I suppose that's the trade-off for the near-zero chain drops you get with single-speed.
The Rotor ring is extremely light thanks to the lightening holes for phase adjustment.
Even accounting for the weight of the chain watcher,
the Rotor still comes out lighter.
I installed the Wolf Tooth 36T on the inner position of the crank.
For the five-arm crank phase, rotating it one more position counter-clockwise would make the gear marking look better.
When you install the 4.5mm nut, it barely contacts the crank.
I measured the Wolf Tooth chainring thickness at 3.7mm.
The Rotor chainring has counterbored holes on the back, and the chainring nuts I was using with it (left and center in the image above)
have a cylindrical portion 3.6mm long, so
in those cases the nut doesn't contact the crank.
With 6.5mm, the nut contacts the crank just right.
I mentioned using a double-speed nut here, but
double-speed nuts also vary in length, and some longer ones will stick out slightly beyond the crank flush line.
Here's a diagram showing how to install a chainring on a five-arm crank (four-arm is more common these days).
In this diagram, the chainring is mounted on the outer position.
Also, some manufacturers install the nut from the outside, but as long as the nut contacts both the chainring and crank, there's no problem.
So with a 6.5mm nut on a 44T or smaller Wolf Tooth,
you get the middle case in the diagram above.
But if the nut is too short and
only bolt threads show directly under the chainring,
the chainring will shift like this.
※I had drawn the shift direction in reverse, but I've corrected it.
As for whether to mount a single chainring on the outer or inner position,
as long as there's no interference with the right chainstay,
mounting it inner-side is better for chainline geometry,
and when mounted on the outer position, if you shift to outer-low, the angular tooth shaping that prevents drops
gets worn away, so inner is definitely preferable.
That said, mounting on the outer side looks cooler (←that's subjective),
and for cyclocross, if you do drop the chain,
having it on the outer means no chain suck, making recovery easier.
I adjusted the gear marking phase as described earlier and
mounted it in the outer position.
I swapped just the bolts for Sugino (スギノ) Torx-head ones.
Since neither chainring has counterbored holes,
neither will sit flush regardless of which position they're in.
Actually, I switched it to the inner side.
On this one, I prioritized chainline over appearance.
The reason I had the Rotor oval on the inner position was
that it was originally a double-speed inner gear, and I had a chain watcher installed, among other reasons,
but if I mounted it on the outer position to make it flush,
the oval shape would flip, so that wouldn't work.
This is my SRAM Rival (スラムライヴァル) crankset,
I've polished the side of the crank arm slightly, but that's neither here nor there—
it's a Wolf Tooth 44T, so no counterbore.
I went with outer position for appearance.
Wolf Tooth chainrings are designed so the chain tooth profile engages differently with outer and inner links alternately,
making the chainring itself essentially drop-proof.
That's why they only come in even tooth counts.
Inner link teeth
Outer link teeth
The tooth-side protrusions seem to do the drop-prevention work.
As for why I'm not using this crankset with the chainring right now,
I acquired a narrow/wide front single chainring that fits a Campagnolo 165mm crank (130mm PCD).
By the way, the Rival I mentioned is also 165mm.
I also upgraded from 44T to 46T while I was at it.
There are chainrings with alternating narrow and wide teeth,
but Wolf Tooth calls them wide/narrow (in that order), while RaceFace calls them narrow/wide.
As long as people understand, either naming is fine.
On this crankset I'm mounting it on the outer side, but
that's because otherwise the chainring won't sit flush against the crank arm.
SRAM RED also has a four-arm crank with a hidden bolt on the back,
and on hill-climb-only bikes and the like, if you mount a single chainring on the inner position,
you end up with a gap between the crank back and the chainring.
The bolt on the crank back is long to begin with, so you can just use it as-is,
and to fill the gap between chainring and crank back via trial-and-error fitting,
Sugino makes what they call a chainring spacer kit (スギノ チェーンリングスペーサーキット) (not exactly designed for this purpose, but it works),
available in 0.5mm thickness and
3.5mm thickness, which can help solve the problem.
The image above shows front single-speed chainring bolts from the same manufacturer, but
these are different parts with different part numbers.
One is for single-speed with the cylindrical portion on the nut side measuring 4.5mm,
while the other one just says "for single-speed."
↑The image on the left is 4.5mm,
and the nut on the right is longer than that, so if we call the left one 4.5mm, this one would be 6.5mm.
The bolt side is also different—
the 6.5mm one has a longer threaded section,
and there's a faint unthreaded zone at the base.
Looking at the Wolf Tooth (ウルフトゥース) chainring,
among my collection of 34T, 36T, 44T, 46T, and 48T rings,
from 46T onward the outer holes on the chainring become counterbored—that is, they have a flush-fit design.
It seems Wolf Tooth's assumption is that you'd mount to the outer chainring position starting from 46T.
Update: I received a comment that there are also 38T rings for 4-arm cranks with counterbored holes.
The counterbore cutoff might vary depending on PCD and intended use (road, MTB, or cyclocross).
Thanks for the comment.
The back side doesn't have counterbored holes.
The chainring bolt sits flush in the counterbored hole.
So the bolt head and chainring are roughly flush with each other.
But with 44T and below (the image shows 36T),
the outer side doesn't have counterbored holes, and
neither does the back side.
Yet Wolf Tooth chainrings are unusually thick, so the shorter chainring bolts (the 4.5mm ones mentioned earlier) aren't long enough to use. So what do you do?
You have to mix and match—use a double-speed nut and single-speed bolt, for instance.
The reverse won't work (I'll explain later).
Here's my bike in the 4kg range.
Currently it has a Rotor (ロター) oval chainring on it.
I don't have strong opinions about ovals, so I could switch to Wolf Tooth, but...
If I went with Wolf Tooth, I could also remove this chain watcher.
As I mentioned before,
Wolf Tooth chainrings are unusually thick, so they're not light.
I suppose that's the trade-off for the near-zero chain drops you get with single-speed.
The Rotor ring is extremely light thanks to the lightening holes for phase adjustment.
Even accounting for the weight of the chain watcher,
the Rotor still comes out lighter.
I installed the Wolf Tooth 36T on the inner position of the crank.
For the five-arm crank phase, rotating it one more position counter-clockwise would make the gear marking look better.
When you install the 4.5mm nut, it barely contacts the crank.
I measured the Wolf Tooth chainring thickness at 3.7mm.
The Rotor chainring has counterbored holes on the back, and the chainring nuts I was using with it (left and center in the image above)
have a cylindrical portion 3.6mm long, so
in those cases the nut doesn't contact the crank.
With 6.5mm, the nut contacts the crank just right.
I mentioned using a double-speed nut here, but
double-speed nuts also vary in length, and some longer ones will stick out slightly beyond the crank flush line.
Here's a diagram showing how to install a chainring on a five-arm crank (four-arm is more common these days).
In this diagram, the chainring is mounted on the outer position.
Also, some manufacturers install the nut from the outside, but as long as the nut contacts both the chainring and crank, there's no problem.
So with a 6.5mm nut on a 44T or smaller Wolf Tooth,
you get the middle case in the diagram above.
But if the nut is too short and
only bolt threads show directly under the chainring,
the chainring will shift like this.
※I had drawn the shift direction in reverse, but I've corrected it.
As for whether to mount a single chainring on the outer or inner position,
as long as there's no interference with the right chainstay,
mounting it inner-side is better for chainline geometry,
and when mounted on the outer position, if you shift to outer-low, the angular tooth shaping that prevents drops
gets worn away, so inner is definitely preferable.
That said, mounting on the outer side looks cooler (←that's subjective),
and for cyclocross, if you do drop the chain,
having it on the outer means no chain suck, making recovery easier.
I adjusted the gear marking phase as described earlier and
mounted it in the outer position.
I swapped just the bolts for Sugino (スギノ) Torx-head ones.
Since neither chainring has counterbored holes,
neither will sit flush regardless of which position they're in.
Actually, I switched it to the inner side.
On this one, I prioritized chainline over appearance.
The reason I had the Rotor oval on the inner position was
that it was originally a double-speed inner gear, and I had a chain watcher installed, among other reasons,
but if I mounted it on the outer position to make it flush,
the oval shape would flip, so that wouldn't work.
This is my SRAM Rival (スラムライヴァル) crankset,
I've polished the side of the crank arm slightly, but that's neither here nor there—
it's a Wolf Tooth 44T, so no counterbore.
I went with outer position for appearance.
Wolf Tooth chainrings are designed so the chain tooth profile engages differently with outer and inner links alternately,
making the chainring itself essentially drop-proof.
That's why they only come in even tooth counts.
Inner link teeth
Outer link teeth
The tooth-side protrusions seem to do the drop-prevention work.
As for why I'm not using this crankset with the chainring right now,
I acquired a narrow/wide front single chainring that fits a Campagnolo 165mm crank (130mm PCD).
By the way, the Rival I mentioned is also 165mm.
I also upgraded from 44T to 46T while I was at it.
There are chainrings with alternating narrow and wide teeth,
but Wolf Tooth calls them wide/narrow (in that order), while RaceFace calls them narrow/wide.
As long as people understand, either naming is fine.
On this crankset I'm mounting it on the outer side, but
that's because otherwise the chainring won't sit flush against the crank arm.
SRAM RED also has a four-arm crank with a hidden bolt on the back,
and on hill-climb-only bikes and the like, if you mount a single chainring on the inner position,
you end up with a gap between the crank back and the chainring.
The bolt on the crank back is long to begin with, so you can just use it as-is,
and to fill the gap between chainring and crank back via trial-and-error fitting,
Sugino makes what they call a chainring spacer kit (スギノ チェーンリングスペーサーキット) (not exactly designed for this purpose, but it works),
available in 0.5mm thickness and
3.5mm thickness, which can help solve the problem.