Answers.Body: <p>This picture might explain the reason:
  <a href="https://i.sstatic.net/eSXIY.jpg" rel="noreferrer"><img src="https://i.sstatic.net/eSXIY.jpg" alt="enter image description here"></a></p>
  
  <p>As you can see, arches form a nice circle to fit round modified plate. All fits well, except the very bottom. Making the bottom edge fit the plate/tile nicely would result in gap with a round piece. The curve of this arch brick isn't full 1/4 circle to make it flush with a tile/plate.</p>
  
  <p>However you may ask "Why didn't LEGO just extend the bottom curve to full 1/4 circle and cover the stud?". This seems to be an obvious solution, but that's a different topic and we may not know which decision caused the part to appear in existing form.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-01-21T11:38:49.057Z
Answers.Text: Thanks for your answer. Yes, raising that bottom stud by half a plate would make a slightly flattened circle. But my exact question is what you leave open at the end of your answer: why is this piece designed the way it is, and is there a piece that completes the circle ( or at least fit smoothly with the arch)? Why didn’t TLG make it the exact inverse of the usual arch?
Answers.UserDisplayName: Phil B.
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-01-21T13:38:58.260Z
Answers.Text: Probably stability and flexibility - [Not](https://www.bricklink.com/catalogItemPic.asp?S=8652-1) [every](https://www.bricklink.com/catalogItemPic.asp?S=31011-1) [set](https://www.bricklink.com/catalogItemPic.asp?S=70828-1) that uses this element wants to create a full circle, and having a stud at the bottom allows them to secure the two together with a tile or plate, rather than butting up against each other.
Answers.UserDisplayName: Zhaph - Ben Duguid
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-01-23T11:09:41.627Z
Answers.Text: @Zhaph, to me your comment seems the only logical answer to this question. I think you should consider expanding your comment to an answer.
Answers.UserDisplayName: Michael Verschaeve
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-01-23T13:27:31.370Z
Answers.Text: @MichaelVerschaeve done.
Answers.UserDisplayName: Zhaph - Ben Duguid
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-01-21T05:09:22.150Z
Answers.LastActivityDate: 2020-01-21T05:17:32.210Z
Answers.LastEditDate: 2020-01-21T05:17:32.210Z
Answers.UserDisplayName: Alex
Answers.Body: <p>Finding a piece that completes a flawless circle can't be done with this element's current design, but...</p>
  
  <p>...If we stick only with <em>Part #2339</em>, we can build an outside frame that changes the direction of the studs themselves in a way that produces the desired effect.</p>
  
  <p><a href="https://i.sstatic.net/lam8O.jpg" rel="noreferrer"><img src="https://i.sstatic.net/lam8O.jpg" alt="enter image description here"></a></p>
  
  <p><a href="https://i.sstatic.net/WNLvP.jpg" rel="noreferrer"><img src="https://i.sstatic.net/WNLvP.jpg" alt="enter image description here"></a></p>
  
  <p><a href="https://i.sstatic.net/oXBbH.jpg" rel="noreferrer"><img src="https://i.sstatic.net/oXBbH.jpg" alt="enter image description here"></a></p>
  
  <p>You could try and contact <em>LEGO</em> <em><a href="https://www.lego.com/en-us/service/" rel="noreferrer">customer service</a></em> directly for their official reason as to why this element is designed in such a fashion as to not produce a perfect circle in conjunction with its inverted twin, because a question this specific could only be verified officially by <em>LEGO</em> themselves, and anything else would seem to be speculation.
  <a href="https://i.sstatic.net/u1qMD.jpg" rel="noreferrer"><img src="https://i.sstatic.net/u1qMD.jpg" alt="enter image description here"></a></p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-01-22T10:58:20.277Z
Answers.Text: Thanks for your answer! I like how you showed how to make a perfect circle using only the non-inverted part. I doubt Customer Service agents at LEGO will have a (canned) answer for this question but it might be something the folks at [The New Elementary](http://newelementary.com) would want to take a look at.
Answers.UserDisplayName: Phil B.
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-01-22T05:43:47.313Z
Answers.LastActivityDate: 2020-01-22T10:55:51.587Z
Answers.LastEditDate: 2020-01-22T10:55:51.587Z
Answers.UserDisplayName: Rin Rio-Oki
Answers.Body: <p>I would assume that this is to do with stability and flexibility of the element, combined with the rectangular nature of the system.</p>
  
  <p>There are a number of uses of the part where it's not used to create a full circle, such as on the <a href="https://www.bricklink.com/catalogItemPic.asp?S=31011-1" rel="noreferrer">tailplane of 31011</a> or the <a href="https://www.bricklink.com/catalogItemPic.asp?S=8652-1" rel="noreferrer">fairing of a Ferarri</a> and having a stud at the bottom allows them to secure the element on the top and bottom, rather than just from the bottom.</p>
  
  <p>If the element was a true quarter circle, the end still wouldn't line up with the system height correctly, so I imagine that the decision was taken to finish it early with a stud, rather than complete it neatly.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-01-24T00:13:53.507Z
Answers.Text: Excellent answer. This makes a lot of sense.
Answers.UserDisplayName: Phil B.
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-01-23T13:27:07.617Z
Answers.LastActivityDate: 2020-01-23T13:27:07.617Z
Answers.UserDisplayName: Zhaph - Ben Duguid
Body: <p>Part <a href="https://www.bricklink.com/v2/catalog/catalogitem.page?id=320#T=S&amp;O=%7B%22iconly%22:0%7D" rel="noreferrer">30099 - Brick Arch 1x5x4 Inverted</a> doesn’t seem to fit into the LEGO system. I cannot find a part that fits on the bottom stud and provides continuity to the concave slope of the arch. A tile is not high enough, and a cheese slope is too high. In other words, the height is 1.5 plates (1/2 a brick). Does anyone know why this is and/or have an example of a LEGO piece that fits this slope?</p>
  
  <p><a href="https://i.sstatic.net/mAxkz.png" rel="noreferrer"><img src="https://i.sstatic.net/mAxkz.png" alt="enter image description here"></a></p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-01-26T22:00:51.393Z
Comments.Text: A Technic half-brick-thin piece such as piece no. 6632 would fit the arch if the slope really is 1/2 a brick higher than the stud.
Comments.UserDisplayName: technicguy1
Tags: <piece-information><compatibility><piece-usage><system>
Title: Why doesn’t part 30099 fit into the System?
UserDisplayName: Phil B.
ThreadText: # Why doesn’t part 30099 fit into the System?
  
  (Asked by: username_0 on 2020-01-21)
  
  Part [30099 - Brick Arch 1x5x4 Inverted](https://www.bricklink.com/v2/catalog/catalogitem.page?id=320#T=S&O=%7B%22iconly%22:0%7D) doesn’t seem to fit into the LEGO system. I cannot find a part that fits on the bottom stud and provides continuity to the concave slope of the arch. A tile is not high enough, and a cheese slope is too high. In other words, the height is 1.5 plates (1/2 a brick). Does anyone know why this is and/or have an example of a LEGO piece that fits this slope?
  
  [![enter image description here](https://i.sstatic.net/mAxkz.png)](https://i.sstatic.net/mAxkz.png)
  
  **Tags:** piece-information, compatibility, piece-usage, system
  
  > **Comments:**
  > **username_1**: A Technic half-brick-thin piece such as piece no. 6632 would fit the arch if the slope really is 1/2 a brick higher than the stud.  
  
  ---
  
  ## 3 answers
  
  ### Answer by username_3 on 2020-01-23. Score: 7 | Accepted answer
  
  I would assume that this is to do with stability and flexibility of the element, combined with the rectangular nature of the system.
  
  There are a number of uses of the part where it's not used to create a full circle, such as on the [tailplane of 31011](https://www.bricklink.com/catalogItemPic.asp?S=31011-1) or the [fairing of a Ferarri](https://www.bricklink.com/catalogItemPic.asp?S=8652-1) and having a stud at the bottom allows them to secure the element on the top and bottom, rather than just from the bottom.
  
  If the element was a true quarter circle, the end still wouldn't line up with the system height correctly, so I imagine that the decision was taken to finish it early with a stud, rather than complete it neatly.
  
  > **Comments:**
  > **username_0**: Excellent answer. This makes a lot of sense.  
  
  ---
  
  ### Answer by username_2 on 2020-01-21. Score: 9
  
  This picture might explain the reason:
  [![enter image description here](https://i.sstatic.net/eSXIY.jpg)](https://i.sstatic.net/eSXIY.jpg)
  
  As you can see, arches form a nice circle to fit round modified plate. All fits well, except the very bottom. Making the bottom edge fit the plate/tile nicely would result in gap with a round piece. The curve of this arch brick isn't full 1/4 circle to make it flush with a tile/plate.
  
  However you may ask "Why didn't LEGO just extend the bottom curve to full 1/4 circle and cover the stud?". This seems to be an obvious solution, but that's a different topic and we may not know which decision caused the part to appear in existing form.
  
  > **Comments:**
  > **username_0**: Thanks for your answer. Yes, raising that bottom stud by half a plate would make a slightly flattened circle. But my exact question is what you leave open at the end of your answer: why is this piece designed the way it is, and is there a piece that completes the circle ( or at least fit smoothly with the arch)? Why didn’t TLG make it the exact inverse of the usual arch?  
  > **username_3**: Probably stability and flexibility - [Not](https://www.bricklink.com/catalogItemPic.asp?S=8652-1) [every](https://www.bricklink.com/catalogItemPic.asp?S=31011-1) [set](https://www.bricklink.com/catalogItemPic.asp?S=70828-1) that uses this element wants to create a full circle, and having a stud at the bottom allows them to secure the two together with a tile or plate, rather than butting up against each other.  
  > **username_4**: @username_3, to me your comment seems the only logical answer to this question. I think you should consider expanding your comment to an answer.  
  > **username_3**: @username_4 done.  
  
  ---
  
  ### Answer by username_5 on 2020-01-22. Score: 6
  
  Finding a piece that completes a flawless circle can't be done with this element's current design, but...
  
  ...If we stick only with *Part #2339*, we can build an outside frame that changes the direction of the studs themselves in a way that produces the desired effect.
  
  [![enter image description here](https://i.sstatic.net/lam8O.jpg)](https://i.sstatic.net/lam8O.jpg)
  
  [![enter image description here](https://i.sstatic.net/WNLvP.jpg)](https://i.sstatic.net/WNLvP.jpg)
  
  [![enter image description here](https://i.sstatic.net/oXBbH.jpg)](https://i.sstatic.net/oXBbH.jpg)
  
  You could try and contact *LEGO* *[customer service](https://www.lego.com/en-us/service/)* directly for their official reason as to why this element is designed in such a fashion as to not produce a perfect circle in conjunction with its inverted twin, because a question this specific could only be verified officially by *LEGO* themselves, and anything else would seem to be speculation.
  [![enter image description here](https://i.sstatic.net/u1qMD.jpg)](https://i.sstatic.net/u1qMD.jpg)
  
  > **Comments:**
  > **username_0**: Thanks for your answer! I like how you showed how to make a perfect circle using only the non-inverted part. I doubt Customer Service agents at LEGO will have a (canned) answer for this question but it might be something the folks at [The New Elementary](http://newelementary.com) would want to take a look at.  
  
  ---
  
  