Replacing seat post - trying to determine diameter from engravings, need guidance
 

I need to replace the seat post of an older bike that I'm restoring.
The seat post has engraved markings, in which one of the lines of text implies the diameter measurement. It starts with an 0, O or circle but with an angled line through the 0,O or circle. Then it reads 25 and then there is a space, then it reads 40.
My assumption is that this is a 25.4 mm post, and when I measure with a ruler it looks to be true (very close to 1"). Unfortunately I don't have a caliper tool to verify this.
I would appreciate some feedback regarding my assumptions.
Thanks

The symbol before the number is an "Ø"; the symbol for diameter.

What kind of bike is it? Is it a BMX of some sort?

Its a Schwinn mountain bike

25.4 AL posts are still readily available.

I'm glad their still available, just need to be reasonably certain that my assumption regarding 25.4mm is correct

Well it's either that or someone decided to randomly engrave the exact diameter of your seatpost, on your seatpost.

25.4 seams a bit small for a mountain post... I sold Schwinns in the 80's and 90's and all of the mountain posts were in the 26mm -27.2mm range.
I haven't kept up with them since they became a department store bike... could very well be they've made some changes to lower the pricing.
I'd recomend measuring the seatpost tube opposed to the seat post... especially if the bike was not yours originally. You'd be suprised how many people replace seat post with the wrong size. A local bike shop should have a seat post diameter gauge they can drop into the frame for you... that is if your willing to take the bike to them.

Use a piece of paper and your mm scale to measure the circumference. Divide by pi and there's your answer. That'll be more precise than you can get measuring the diameter with a linear scale.

I take a cheap drawing compass and open it till I can just fit it around the seatpost. Then I just place the drawing compass on a ruler. Its pretty darn precise.

But, yeah, 25.4 sounds reasonable.

25.4, aka 1" is also made in a chrome-moly steel , I have one left over from single speed build
using a Schwinn Mesa Runner, it, post, came thru a 'red line' dealer ,
SBS Seattle bike, distributor it is strong ..
I had a foot of post out of the frame.
thicker wall seat tube = smaller ID and seat post.

Wind a dollar bill twice around the post on a very shallow spiral. Draw a straight line across the layers. Unwind and measure from the first mark to the third (about 6-1/2") with a mm scale, divide by 6.28 (twice Pi) and there's your diameter.

Use that as a cross check, but if it says ø25.4 it's 25.4mm, since there's no size with similar looking digits. (it's easy to misread a 28.6 for 28.8 with faint markings, but that kind of error isn't possible with s 25.4)

"O" with a diagonal slash through it is the technical symbol for diameter.

Chombi

You can get a simple caliper at Sears for $8. You'd use it for many other jobs as well.

I also have one of those Schwinns; the components are better than dept store, but not top quality. I like it for bumming around a bit. Seatpost size on mine is 25.4.

+1 Either buy an inexpensive caliper (Harbor Freight has a digital one for $10), or take it to a shop. Sizing via the internet is prone to error.

Amen
 

Skillfully understated, yet on target.
Kudos :roflmao2: