There are indeed 2 versions of indicated hubs. One is called standard version and the other one is Super Light (SL) version so the letters SL distinguish one version from another. The reason why SL version was developed is due to its lower weight compared to standard one.

The weight of A291SB-SL is 60 grams while standard A291SB weights 76 grams.
The weight of F482SB-SL is 228 grams while standard F482SB weights 245 grams.
It might seem just small weight difference but for road hubs/wheels the weight is crucial so each gram counts.

Lower weight for SL was achieved thanks to this:

• SL version has smaller and lighter bearings than standard version
• SL version has weight saving cut-out holes in its flanges while standard hub doesn’t
• SL version has slightly different shape than standard one (rear hub)

Pictures below show the difference (black hubs- standard version, red hubs - SL version):

The bearings used in SL hubs are as follows:

• A291SB-SL: 2pcs of #689 in the hub shell
• F482SB-SL: 1pc of #6802 and 1pc of #15267 in the hub shell

The bearings used in standard hubs are as follows:

• A291SB: 2pcs of #699 in the hub shell
• F482SB: 1pc of #6802 and 1pc of #6902 in the hub shell

Both versions have another 2pcs of bearings inside of their cassette bodies.

Important: Both versions have the same axle, the same side caps and also the same cassette body for rear hub F482SB/F482SB-SL. But there are different side caps for front hub A291SB/A291SB-SL, therefore make sure you specify to seller which type of hub you have when ordering the side caps for your front hub.