SPR

From YoYo Wiki

SPR stands for Spacer Pad Response. It is a bearing and response system produced by Buzz-On, intended to allow easy modification of yo-yos. The SPR is, essentially, oversized bearing spacers. The bearing is held between the two spacers by a small bearing seat. The rest of large brass spacer is smooth and flat, allowing a yo-yoer to place any of a variety of friction stickers on it.

[edit] Sizes

The SPR originally was introduced in only one size, the large C bearing, but it now comes in three different sizes: large, medium, and small. SPR kits can easily be placed in most yo-yos that use bearing spacers to allow the use of a different response option or a different sized bearing than the yo-yo originally had. Buzz-On currently produces most of their own line of yo-yos with SPR spacers recessed into the sides of the yo-yo.