Will this combo fit my CS-490 Echo ?

No, the 490 is a .325 pitch chain and this is 3/8"

can i fit this on a echo 310 ?

Thank you for contacting Oregon Tool Noah. The 20" Oregon bar and chain combo, part number 27850 will not fit your Echo CS-310. The longest bar and chain combo that we offer for your application is 18", part number 540394. Please contact one of our Technical Services Experts at 1-800-223-5168, option #1, if you have further questions.

Will it fit my solo 651sp?

Hello, Otto. Thank you for your interest in the Oregon® brand. According to our system, the part number provided isn’t a match for your Solo 651SP. The 651SP can be set up set up to run either a 3/8" standard pitch cutting system or a .325" pitch cutting system. Before purchasing a bar and chain combo please make sure you know which chain pitch your saw is set up for. The correct .325" pitch bar and chain combo for your application is part number 579810. The correct 3/8" standard pitch bar and chain combo for your application is part number is 584818. For further assistance, we recommend speaking directly with one of our experts at Oregon® Technical Services. They handle calls like yours all the time and are ready to help you any way they can. You can reach them between the hours of 6:30 a.m. and 4:00 p.m. PST at 1-800-223-5168, option 1. You can also email them at oregon.support@oregontool.com.