How to number the parts in the drawings? is there any tools available for the same for maintaining uniformity?
If you are submitting a patent application to the U.S. Patent Office, then according to the Manual of Patent Examining Procedure 608(p): (1) Reference characters (numerals are preferred), sheet numbers, and view numbers must be plain and legible, and must not be used in association with brackets or inverted commas, or enclosed within outlines, e.g., encircled. They must be oriented in the same direction as the view so as to avoid having to rotate the sheet. Reference characters should be arranged to follow the profile of the object depicted. (2) The English alphabet must be used for letters, except where another alphabet is customarily used, such as the Greek alphabet to indicate angles, wavelengths, and mathematical formulas. (3) Numbers, letters, and reference characters must measure at least .32 cm. (1/8 inch) in height. They should not be placed in the drawing so as to interfere with its comprehension. Therefore, they should not cross or mingle with the lines. They should not be placed upon hatched or shaded surfaces. When necessary, such as indicating a surface or cross section, a reference character may be underlined and a blank space may be left in the hatching or shading where the character occurs so that it appears distinct. (4) The same part of an invention appearing in more than one view of the drawing must always be designated by the same reference character, and the same reference character must never be used to designate different parts. (5) Reference characters not mentioned in the description shall not appear in the drawings. Reference characters mentioned in the description must appear in the drawings.
Generally, while not required, it is customary to group numbers relative to the description in the disclosure so that someone reviewing the patent does not have to jump around the disclosure and the drawings to understand the subject matter being disclosed. Personally, I use even numbers for reference purposes. That allows me to come back later to use an odd number if I had forgotten to label a feature.
Patent Offices in other countries may have differing requirements. I would refer to their websites or contact them directly for more information.