Answers.Body: <p>I can give you some help, especially if you are talking about 2x4 bricks.  Last year, I embarked on a bit of a history project to trace the design changes in Lego, by looking at the 2x4 brick, from 1949 to today. (Such as changes in the tubes, like the slots you mention!) I talked to several very helpful collectors (some here on Bricks beta!), who gave me lots of helpful information.
  I distilled it all down into this article:</p>
  
  <p><a href="http://snakeandboris.blogspot.com/2016/06/a-short-history-of-lego-brick-1949_6.html" rel="nofollow noreferrer">http://snakeandboris.blogspot.com/2016/06/a-short-history-of-lego-brick-1949_6.html</a></p>
  
  <p>(This link goes to Part 2 of the article, because it contains a link for Part 1.)
  Keep in mind, though, that not all dates with Lego changes are hard-and-fast.  You will see a few "c." meaning it was AT or AROUND that time--because as Lego changed molds, they didn't do it all at once, across the whole world. They used the old molds for their normal lifespans.
  There are even MORE sub-variations than what I have found, and there are links at the end of my post to some other good sources of information.
  Good luck! One thing about this hobby I can tell you, there are lots of knowledgeable and kind folks to help you!</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-07-28T20:26:13.100Z
Answers.LastActivityDate: 2017-07-28T20:26:13.100Z
Answers.UserDisplayName: sampoerna quatrain
Body: <p>I have a bunch of bricks from my childhood, some have grooves in the tubes underneath, some have the old style bubble logo, some have square holes under the plates. I am interested in general ages of each.</p>
  
Tags: <piece-information><history>
Title: When did LEGO have a groove in the center tube underneath?
UserDisplayName: Beth Hanson
ThreadText: # When did LEGO have a groove in the center tube underneath?
  
  (Asked by: username_0 on 2017-07-25)
  
  I have a bunch of bricks from my childhood, some have grooves in the tubes underneath, some have the old style bubble logo, some have square holes under the plates. I am interested in general ages of each.
  
  **Tags:** piece-information, history
  
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  ## 1 answers
  
  ### Answer by username_1 on 2017-07-28. Score: 4
  
  I can give you some help, especially if you are talking about 2x4 bricks. Last year, I embarked on a bit of a history project to trace the design changes in Lego, by looking at the 2x4 brick, from 1949 to today. (Such as changes in the tubes, like the slots you mention!) I talked to several very helpful collectors (some here on Bricks beta!), who gave me lots of helpful information.
  I distilled it all down into this article:
  
  <http://snakeandboris.blogspot.com/2016/06/a-short-history-of-lego-brick-1949_6.html>
  
  (This link goes to Part 2 of the article, because it contains a link for Part 1.)
  Keep in mind, though, that not all dates with Lego changes are hard-and-fast. You will see a few "c." meaning it was AT or AROUND that time--because as Lego changed molds, they didn't do it all at once, across the whole world. They used the old molds for their normal lifespans.
  There are even MORE sub-variations than what I have found, and there are links at the end of my post to some other good sources of information.
  Good luck! One thing about this hobby I can tell you, there are lots of knowledgeable and kind folks to help you!
  
  
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