Can someone please explain tube size naming to me?

Since I've been looking all over the web at different rocket sites, I see different naming conventions for body tube sizes:

I know the standard BT system. (BT-50, BT-55, BT-60, etc.) Example

But then Semroc does this with motor mounts (#5, #10, #16, etc) Example

Anyone know how to decode their motor mount listings? I emailed them and asked 5 days ago with no response.

I'm not completely sure, but I have a guess: Since a #5 to #8 engine mount fits a 0.5" diameter engine, and a #7 to #10 fits a 0.7" diameter engine, I would guess that #8 is approximately ) 0.8", and #10 is 1".
If I'm wrong, please correct me, but that explanation seems to make pretty good sense. :wink:

Semroc seems like a really good site, but they lost a sale because I couldn't figure out what the mount for an E engine in a BT-70 tube was.

John Brohm's estes body tube list is a pretty interesting read.

https://www.rocketshoppe.com/info/Estes_Body_Tube_List_3.1.pdf

Everything makes sense in high-power: they just give the dimensions. The namings for low-power stuff is confusing as all heck, though.

Green Jello said:

Semroc seems like a really good site, but they lost a sale because I couldn't figure out what the mount for an E engine in a BT-70 tube was.

Click to expand...

Everything you need to make your own motor mount is available. An Estes E motor is 24 mm wide. All 24 mm motors fit in a BT-50 tube. BT-50 is listed on Semrocs Body Tubes page(s).

The centering rings acommondating the outside diameter of a BT-50 tube to the inside diameter of a BT-70 tube can be found on the centering rings page(s),pg. 3, 5th row down.

No problem finding the materials, Semroc listed them all.

bradycros said:

Everything you need to make your own motor mount is available. An Estes E motor is 24 mm wide. All 24 mm motors fit in a BT-50 tube. BT-50 is listed on Semrocs Body Tubes page(s).

The centering rings acommondating the outside diameter of a BT-50 tube to the inside diameter of a BT-70 tube can be found on the centering rings page(s),pg. 3, 5th row down.

No problem finding the materials, Semroc listed them all.

Click to expand...

I realize that, but I just wanted to buy a motor mount kit and make it easy. I'm positive they had the parts. Just saying their website kinda sucks.

The numbers you are referring to come from Centuri - Estes main competitor back in the late 60s & early 70s. Estes created the BT numbering system (BT-5, BT-20, BT-50, etc.) which was pretty arbitrary. Centuri, on the other hand, used the English measurement system to label their tubes as ST-7 (which was about .7 inches diameter - which was the standard motor tube and pretty much the same as the BT-20). The ST-8 series was .8 inches in diameter and the ST-10 series was 1 inch in diameter. But if you will look further, you will see that Semroc also carries Estes sized tubing, nose cones and accessories such as centering rings, motor blocks and so forth. You need to go a few pages in and look for BT numbers for your centering rings. On the 3rd page of centering rings is the BT-50 to BT-70 centering ring (RAH-5070) - you get a package of 6 for $4.15.

bradycros said:

Everything you need to make your own motor mount is available. An Estes E motor is 24 mm wide. All 24 mm motors fit in a BT-50 tube. BT-50 is listed on Semrocs Body Tubes page(s).

The centering rings acommondating the outside diameter of a BT-50 tube to the inside diameter of a BT-70 tube can be found on the centering rings page(s),pg. 3, 5th row down.

No problem finding the materials, Semroc listed them all.

Click to expand...

Green Jello said:

I realize that, but I just wanted to buy a motor mount kit and make it easy. I'm positive they had the parts. Just saying their website kinda sucks.

Click to expand...

I disagree, Semroc's web pages rocks.

They (Semroc) definitely need to work on their product descriptions, though. Looking at centering ring descriptions, there are several with headings that don't match the description and a few that the descriptions are not self-consistent.

For example:
This - Is it a BT20 in BT55 or a BT50 in BT55?
This - "center three BT-20 tubes inside a BT-60 tube. Especially useful for making an dual engine mount..." - so is it a dual or triple engine mount?
etc...

Seems a bit of cleanup/maintenance may be needed. That said, they definitely have an excellent selection of products and reasonable prices.

Green Jello said:

Semroc seems like a really good site, but they lost a sale because I couldn't figure out what the mount for an E engine in a BT-70 tube was.

Click to expand...

Why don't you just buy a BT-50 and use it as an engine mount tube? I don't get you at all?? There's 100's of places to buy tubing. Go to LOC's website and buy some of theirs. It's thick wall and will last longer than your standard engine tubes? Is it really that difficult? Buying an engine mount kit is probably the last route you want to take. There's nothing to making your own. Cut a tube to whatever length you want and then glue some rings on. You can buy the rings anywhere. Why don't you just ship the parts to someone on here and they will put the rocket together for you and even paint it. all you have to do is install the chute and and motor and push the launch button.

Look I'm sorry for being so blunt, but dude you need to do the leg work and figure it out. It's part of the hobby and it's a learning process. Some of your post are things that take hardly next to any effort at all to do. I for one have posted sites that you can go to to learn how to build rockets and have hundreds of articles on building rockets.

https://www.apogeerockets.com/Newsletter/newsletter_archive

"How To" Video's

https://www.apogeerockets.com/Advanced_Construction_Videos/All

Watch the videos. There's a lot of information there...there's one on how to make a motor mount.

AfterBurners said:

Why don't you just buy a BT-50 and use it as an engine mount tube? I don't get you at all?? There's 100's of places to buy tubing. Go to LOC's website and buy some of theirs. It's thick wall and will last longer than your standard engine tubes? Is it really that difficult? Buying an engine mount kit is probably the last route you want to take. There's nothing to making your own. Cut a tube to whatever length you want and then glue some rings on. You can buy the rings anywhere. Why don't you just ship the parts to someone on here and they will put the rocket together for you and even paint it. all you have to do is install the chute and and motor and push the launch button.

Click to expand...

They lost my sale because I was trying to order ALL the parts I needed from ONE vendor. I have never built anything but LPR Estes kits and this was my first scratch built project. I don't have 1% of the knowledge that most of you have here and they (Semroc) weren't answering my emails. Is that ok with you? How about you lose some of the attitude? Since then I have placed 2 orders with Semroc and even paid $10 to be in their club. Seriously....what the heck man? Do you have some kind of financial interest in Semroc?

First of all you're not going to find everything from one vendor most of the time, but I understand wanting to purchase everything from one site. No I don't have financial interest in SEMROC, but I can honestly say that I have done business with them before and always had great service and they sell quality parts. I'm sure I'm not the only one who has had a great experience with SEMROC. Why don't you try Hobbylinc...they sell just about everything you need for building rockets. As far as your building skills well LPR and MPR in most cases are the same except that the parts are slightly larger, but the same skills you have to build LPR can be carried over to MPR.

HERE I did the research for you:

https://www.brshobbies.com/catalog....d32793/Sunward_24mm_Engine_Mount_Kit_for_BT70

If you can look through the site you will find more stuff on there to build your rocket. I don't have an attitude You should tone it down.

You don't have an attitude? You basically just told me to give up and pay someone to build my stuff for me. Seriously....go back to the original post in this thread and read it again. It was a pretty simple question. If you don't want to help answer it, and my minor criticism of the all mighty Semroc offends you, then I suggest you just ignore me from now on.

You should really refrain from bashing companies on here like SEMROC. There may be a time in your hobby that they may be the only place buy something from. Don't blame SEMROC or put them down for not getting back to you. You're not the person only out there that has written emails or left phones messages. I'm sure they will contact you. Most of these businesses are in fact owner/family operated and they can't get to everyone all at once. Maybe you should exercise more patience in your research.

And to answer your question no I don't have an attitude. The way to present yourself you lack any motivation to do any of the research yourself. You have a computer and access to every model rocket supply company. I myself just posted a few links where you can buy a motor mount and other supplies and as well articles and "how to" videos, but that seem to go right over your head. You want to bash me and I tried help you because you seem incapable of doing it yourself.

I'm sorry but that's just how I see it. Good luck in your build.

I'm done here.

One note to explain the lack of response: SEMROC is legendary for their responsiveness, but one of the major rocketry events of the year has been going on and they posted in Vendors that they were attending and would be out of office. Usually you will get lightning quick responses. Congrats on becoming a SAM and you will become spoiled by their insta-ship routine. Sometimes it seems like they ship before I place an order... :wink:

Marc_G said:

One note to explain the lack of response: SEMROC is legendary for their responsiveness, but one of the major rocketry events of the year has been going on and they posted in Vendors that they were attending and would be out of office. Usually you will get lightning quick responses. Congrats on becoming a SAM and you will become spoiled by their insta-ship routine. Sometimes it seems like they ship before I place an order... :wink:

Click to expand...

I have gotten the in process and then shipped email in the course of about 5 minutes. Had it on my doorstep the next day. But, true, I live about 1.5 hours from them...

Green Jello: did you bother to send them an e-mail with a question about the parts you need? They are very good at helping folks out and have often sent the correct parts to fit what someone had ordered. They sent me a piece that they thought I needed, but I already had it.
Their website is complicated BECAUSE they offer so many parts to match older and current Estes, Centur, FSI, etc parts.

Ask them instead of complaining here. Learn before you vent.

SEMROC SAM#0003

Buzzard said:

Green Jello: did you bother to send them an e-mail with a question about the parts you need? They are very good at helping folks out and have often sent the correct parts to fit what someone had ordered. They sent me a piece that they thought I needed, but I already had it.
Their website is complicated BECAUSE they offer so many parts to match older and current Estes, Centur, FSI, etc parts.

Ask them instead of complaining here. Learn before you vent.

SEMROC SAM#0003

Click to expand...

Yes. I sent them 5 or 6 emails. Some of them went unanswered, while some of them were answered days later. I have since learned that the minor lapse in their legendary service was probably because they were at the launch in NY all week.

Let me be perfectly clear here. I am not complaining of "venting" about Semroc here. I realize they are probably the best vendor out there. Since I had these problems, I have places two part orders with them and even joined their club for $10. Would I have done that if I didn't feel confident in them?

Look at the original question in this thread. That's what this is all about. That size numbering system is just odd and I didn't understand it.

I replied to the same question here:

https://www.rocketryforum.com/showt...t-come-up-with-the-body-tube-numbering-system

Look at plumbing. A 1-1/2" dia pipe isn't 1.5", a 1/8" dia pipe is almost 3/8". Lumber too; a finished 6x4 is really 5.75 x 3.75.. Wire dia? A 16AWG isnt the same as a 16g SWG. Sheet metal also has weird sizes, and different scales that don't match..
I've had one technician / helper bring me a 1/4" wrench for the 1/4" bolts we were tightening.. (you really want a 7/16"!)

It seems each have their own sets of 'standards'. We just learn to work with them..

The great thing about standards is that there are so many of them!

It is too bad they can't come up with a universal system.

Uh, they did... its called Metric & ISO/DIN.. Toss in CE if you want a bit more standardization for your toys & electronics..

Sorry, don't mean to make a snide remark, a smug comment, or hop on a pedestal.. Being a Canadian, i need to design to meet the US market, yet use parts from overseas.. So I'm using both metric & imperial measurements, and converting between them daily.. Metric is widley used once you get outside the US border / off the N. America continent..

Again, this isn't a 'smart-alek' remark, and I don't intend it to be. ISO standards are accepted in most coutries outside of N america..

I have cabinets that measure 39" x 39". Why not jsut a 36" x 36" NEMA 4 cabinet? Because the cabinet manuf is European, and is one of the largest, and it's a standard 1m x 1m cabinet, rated to IP65..

Don't apologize for a second Dr. Wogz. The US pulled an epic failure for not changing to the metric system from our retarded system back in the 70s. I hate that we use it and take it as a position of great national embarrassment.

dr wogz said:

Uh, they did... its called Metric & ISO/DIN.. Toss in CE if you want a bit more standardization for your toys & electronics..

Sorry, don't mean to make a snide remark, a smug comment, or hop on a pedestal.. Being a Canadian, i need to design to meet the US market, yet use parts from overseas.. So I'm using both metric & imperial measurements, and converting between them daily.. Metric is widley used once you get outside the US border / off the N. America continent..

Again, this isn't a 'smart-alek' remark, and I don't intend it to be. ISO standards are accepted in most coutries outside of N america..

I have cabinets that measure 39" x 39". Why not jsut a 36" x 36" NEMA 4 cabinet? Because the cabinet manuf is European, and is one of the largest, and it's a standard 1m x 1m cabinet, rated to IP65..

Click to expand...