I need to replace the fishing tip guide on my spinning rod.  Is there a way to tell which size I need? I have a lews Mach speed stick  https://www.lews.com/rods/mach

Is it off the rod now?  If yes, that's good.  If not, use only a little heat and it will come off if Lews used hot melt.  If it doesn't readily come off, take it to a pro builder.  Getting an epoxied one off is not easy and blank can easily be damaged.  When I say a little heat, if done right the tiptop will be uncomfortable to touch, but hardly.  I hook a rubber band on to the tiptop and put tension on it, when it gets hot enough it will slide off.  IN ONLY A FEW SECONDS OF HEAT FROM A LIGHTER.  iF IT DOESN'T READILY COME OFF, STOP.

 

Ask Lews for the size.  And  brand/model number.

 

Or measure the OD of the tip for the tube size.  need it in 64's.  The ring size is tougher, you must measure the OD of the ceramic ring, not the ID.  Use a micrometer or similar for this.  Need it in mm.  Then order the next higher tube size from what you measure with the right ring size in mm.