N28A Ground Valve Sleeves sizes: .630-.700

    These steel sleeves are used to straighten bent and out of round pistons. The sleeves have been bored and then honed to the exact sizes used when the valve casings were manufactured. They are not adjustable. This is a forming die.

For Sizes Not Listed or Special Sizes Please Enter Desired Size in the Note Section on the Check-out Page.

The recommended procedure for use:

    Remove the valve cap, finger button, stem and guide from the piston. Select the proper diameter sleeve and push the piston all the way in so the main body of the piston is completely covered by the sleeve. Hold this complete assembly in the palm of your hand. Use a F5 rawhide mallet or F11 canvas mallet and strike the outside of the steel sleeve many times, rotating the sleeve in your hand as you go, so hammer blows strike the sleeve all the way around. Continue this procedure until the piston works freely in the sleeve.

ORDER THE EXACT SIZE. THESE MANDRELS ARE NOT ADJUSTABLE 
TO ORDER THE CORRECT SIZE—

Order by the O.D. of the piston. Example: Yamaha .664”. Due to the differences in manufacturing over the years it is highly RECOMMENDED to measure the valve piston.

These mandrels are divided into 3 size groups:

(N28A Part # for sizes: .630-.700, N28C: .701-.885,  N28D: .888-1.400) 

N28A For cornet and trumpet
N28C For alto horn, valve trombone, baritone and euphonium
N28D For sousaphone, Tuba, Bari 

For Sizes Not Listed or Special Sizes Please Enter Desired Size in the Note Section on the Check-out Page.