New- QX4600 Mainspring-More Power Than before but Docile...... This spring is all new ( 10-2009) designed for the new TX200's with the .558-.560 OD guides ( latest model- Works well on all .545-.560 guides from prior AA variations)  For max life in most spring guns use mid weight pellets only. Suggested weights for a .177 TX200 is 7.4-9.0 gr max. With 7.9 to 8.6 grs being ideal as long as they are a good fit in the barrel. 32 x.120" ID .560 set