Instruction: Answer the given question by extracting information from the supporting document.

Input:
Question: Is the rubber on the wheels gray or black? The title says gray but the picture shows black.
Document: The main problem is that the wheels and bumpers smell of burning rubber and industrial solvent. They should not be used inside the home. They might be okay for a garage or storage, but I could not use them in my craft room as I planned because the smell was filling up the whole house (even before I installed them).The wheels are very solid. They were not gray as described in the item title.
(Installation instructions for Alera caster kit: you have to insert a dowel or other long, thin object into the open end of the shelving piece, turn it upside down and tap or drop it onto that object to push the end plug out. Have a rubber mallet on hand to tap the casters into place as the fit is snug.)
These casters are no joke. They are way overbuilt and do a great job of adding mobility to 500+ pound shelves.Beware you need a 3/4 X 48 dowel to install them on "2x Alera SW504824BL Industrial Wire Shelving Starter Kit, 4 Shelves, 48w x 24d x 72h, Black" shelves.
The wheels are heavy duty and easily installed on the shelving unit. I recommend these for anyone needing mobile shelving units.
These caster wheels are sturdy. I like that they lock. I wish it did not cost so much. I gave it 4 stars because of the high cost.
Got this to go with the Wire shelving  and they are good. Wheels good size, well made,prompt shipping, and easily installed. Locking whells are always a good idea. Recommendable
Then instead of the rounded cap at the top, I have the levelers at the top. If I ever want to use the shelf unit without the wheels, just reverse the process. The wheels are solid, and very large with respect to the shelf. So they don't get caught up on floor irregularities or carpet. The breaks work easily and hold firm.
I ordered this caster kit to go on the Alera Instrustrial Wire Shelving 48w x 24L, which is a very heavy well built unit. The wheels were very easy to install and are even more substantial then I could have hope for. I have a very similiar wire shelving unit that I purchased caster for from a local &#34;box&#34; hardward store years ago.
I installed these with the ALESW504824BL shelving starter kit.The wheels go on easily once you figure out how to remove the bottom-stops in the shelf-tubing. My trick was to put a dowel rod inside the tube and throw it on the ground (dowel side first). The stop popped off easily.There are two wheels with brakes and two wheels without - that's a bit hard to see by looking at the Amazon image.
The Alera wire shelving tells you to take out the levelers on the bottom of the shelf posts, 'poke out' the threaded inserts with a "dowel or broomstick", and then insert the wheels. Not sure why the instructions say that because I just turn the posts upside down, pry off the top cap--MUCH, MUCH easier than poking out a perfectly good threaded insert on the other end--and put the wheel in the TOP of the post and use the post upside down.
Answer: Black is the  color of Caster rubber wheels   # SW590004