Image courtesy of www.steel-vintage.com
In the early 1980’s Colnago began experimenting with crimping main frame tubes to increase stiffness. In the mid 1980’s, Colnago and Gilberto Columbus developed the Gilco Master tube profile which was a round tube that featured four distinct symmetrical flutes through the central section of the tube and resembled a 4-sided star. This tubing was used to build a new bicycle simply called the Colnago Master.
The Gilco Master tube profile outlasted all other Colnago tube designs and can you can still order a modern Master steel frameset in 2019.
Before you start with the identification process, you should start here;
How to identify a Colnago vintage bike.
Special features of a Colnago Master.
As mentioned previously, Gilco Master tubing is the special feature of this frame and it’s unique shape is easy to identify. These specially profiled tubes were used in all 3 tubes of the front triangle ie. top tube, seat tube and down tube.
This tube shape was so successful it was a patented design by Colnago and evolutions of if were used in many of Colnago’s more modern carbon fibre lugged high performance frames.
Some of the original Colnago Arabesque models are built using Gilco Master tubing (just like the modern Arabesque). The difference being the Arabesque is built with ornate lugs.
Here are some pictures showing the profile of the tubes. Images courtesy of www.steel-vintage.com
Gilco Master 4 sided profile down tube. 
Gilco Master 4 sided profile seat tube.
General features of a Colnago Master.
These images demonstrate the features typically found on a Colnago Master frame. Images courtesy of www.steel-vintage.com
Rear brake cable routed over top tube. 
‘Colnago’ lettering and club symbol on down tube lug.
Braze-on shifter mounts.
Club symbol and ‘Colnago’ lettering on sloping fork crown. 
Club symbols on top of bottom bracket. 
Club cut-out under bottom bracket. ‘Brev Colnago’ lettering.
Shift cable guides under bottom bracket. No chain stay bridge.
Braze-on front derailleur mount. 
‘Colnago’ lettering on seat stay caps. 
Club symbol on top of seat stay bridge
What is a Colnago Master Più.
A Piu version of the frame featured the rear brake cable routed inside the top tube instead of on top of the top tube. Several other models were released in this style or could be custom ordered with this feature ie. Colnago Super Più etc. Here are some images of a Colnago Master Più. Images courtesy of www.raydobbins.com.
Colnago Master Piu. 
Rear brake cable enters top tube just behind head tube. 
Rear brake cable exits top tube in front of seat tube.
Later Versions of the Master
Models released around 1988 featured the straight Precisa front fork rather than the traditional curved forks you see in the catalog image above. A set of biddon cage bosses were also added to the seat tube for mounting a second water bottle.
 | Models released from the early 1990’s featured different lugs like the one shown here. |
Colnago Master Equilateral
Image courtesy of Road Bike Action Magazine
The Colnago Master Equilateral frame is quite rare as it was only in production for a year. I couldn’t find it listed in any of the Colnago catalogues I have on file. Further research online suggests that possibly only 85 frames were ever manufactured. Road Bike Action magazine wrote an interesting article about this bike along with close-up photos.
Interested to see how a 1984 Colnago Master compares with a 2014 Cervelo R5? I have written an in depth article on how these 2 bikes compare.
Colnago Literature.
The following websites have a large selection scanned Colnago literature including reviews, catalogues and brochures.
Article References.
I hope you found this article interesting. I have listed the following website pages as general references.
www.steel-vintage.com
www.raydobbins.com
Disclaimer!
Please remember that this information is only to be used as a guide.
I consider myself an enthusiast, not an expert. The information I have presented in this article is based on my many hours of online research.
In addition, there will always be frames that don’t quite match the characteristics of a particular model as they could have been a custom build, prototype etc. Note: forks can also be swapped between different frames.
About Me.
I have been riding and working on my own bikes for many years now. I wanted to share my experiences, knowledge and research with others. My aim is to inspire people to get involved in all aspects of this amazing sport. Cheers.
Comments.
I welcome reader feedback in the comments section. Should you wish to suggest an amendment, please include a note advising the source of your information so that myself and other readers can ascertain the accuracy of your information. Note: Trolling or argumentative comments will be removed as they are counter-productive.
Thanks for this information.
Now I can be ‘sure’ that my Colnago seems to be a later version with the typical tubes.
In the rear right drop out there is marked C37 054. Would you know if that has something to do
with the year of production or with the type?
Many greetings,
Jan
Hi Jan, glad to hear this article was of help. In regards to your frame number, it’s an interesting question, but I don’t know. On the older frames, I suspect it is just a serial number. If any records still exist, they’re probably lying forgotten in some dusty archive.