We have designed a Gym and Wallet Friendly indoor Weight Throw.  
 
Using a custom bag made of high strength polyester webbing the harness is set for up to a 10 inch slam ball.  Buy it with the ones we use - Rep V2 and Rage slam balls or supply your own.
 
It has added straps that hold the slam ball down in the harness for a secure fit.  The polyester straps are 4,500 lb and 12,000 lb rated for strength.  Polyester does not stretch and wears better than the nylon or cotton used in other harnesses.  They are water resistant and can be thrown outdoors onto grass and do not cause the massive divots that normal weight throws do.  If they get dirty just wash them off.  The swivel is stainless steel and the handle is painted and heat cured.
 
When thrown inside the Weight Throw lands with a thunk and the slam ball absorbs the impact with little bounce and a roll rather than the BANG of a normal weight throw and the clatter of handle and hard weight on the gym floor.  If the handle is between the slam ball and the floor the pliable slam ball takes the impact rather than the gym floor.
 
The handle is made from 1144 Stressproof 3/8" steel rod with over 100,000 psi yield strength.  That is twice to three times normal handles made in China.  We use a solid steel triangle support piece fully 360 degree welded for added durability, break and bend resistance. 
 
Nylon shoulder washers are used in the handle to give a solid smooth rotation.  Spares are supplied.  The shoulder bolts us a 5/16" open end wrench to secure rather than the typical slot that strips and becomes problematic.  We recommend using purple Loctite on the shoulder bolts for a secure connection that will not come loose.  DO NOT USE RED LOCTITE.  You will need a torch to get them loose.
 
We use D rings for the transition to the swivel so that wear on the straps is even across the entire strap.  Typical O rings wear on the edge and once the edge is worn away the strap is compromised and quickly gets to be dangerous to throw.
 
This makes a great practice implement.  Inexpensive and preserves the basketball floor or the mats that it hits.  Controlled after roll and bounce.  Using the slam ball that is rugged and uses sand instead of lead ls a great safety factor.  And if the slam ball breaks after hard sustained practices it is easily replaced for less than $60.
 
The two compromises are that the weight throws are about 1.8 lbs heavier than regulation and a few inches longer than the 19" allowed.  But the extra weight and length almost balance each other out so that the feel is close to a regulation weight throw.
 
Shipping is flat rate via US Postal Priority mail.  One weight throw fits in the large priority box and ships for $21.00.