Question 1

will this product fit the SV305 pro?

Accepted Answer

I'd contact SyBony directly - they make both the SV305 camera and this helicoid.  The "1/25in" spec is common for telescope eyepiece accessories including cameras, but this version (they make others) of the helicoid has 42x0.75mm threads (T-mount) on both sides, implying another model or an additional adapter.

Question 2

what is the outside diameter?

Accepted Answer

Dear customer ,
Thanks for your contact.
1.77inch.

For accessories;we provide 2 months warranty;within 2 months;you can return for refund or replacement.If you have any other questions about warranty;please contact us freely;we will work with you win to win.
If my reply still doesn't answer your question well or you want to know more details about this product,please contact us by message on Amazon. Because the customer's message can be seen in the first time on Amazon, and will solve the problem as soon as possible. Once I receive your response, I will try my best to answer your questions. 
Sincerely look forward to your reply.
Best wishes !
Kelly

Question 3

Will this fit on my 1.25" eyepiece / camera?

Accepted Answer

Dear customer ,
Thanks for your contact.
SVBONY Extension Tube has M42x0.75 male thread and M42x0.75 female thread. It cannot be directly connected to the 1.25-inch eyepiece, but can be connected to the camera through an adapter ring. Generally used to solve spacing problems in astrophotography.

For accessories;we provide 2 months warranty;within 2 months;you can return for refund or replacement.If you have any other questions about warranty;please contact us freely;we will work with you win to win.
If my reply still doesn't answer your question well or you want to know more details about this product, please contact us by message on Amazon. Because the customer's message can be seen in the first time on Amazon, and will solve the problem as soon as possible. Once I receive your response, I will try my best to answer your questions. Sincerely look forward to your reply.
Best wishes !
Kelly

ASIN	B07BKYQF1H
Additional Features	Extension Tube M42x0.75
Best Sellers Rank	#153 in Telescope Photo Adapters
Brand	SVBONY
Compatible Devices	Cameras with M42x0.75 thread
Customer Reviews	4.5 out of 5 stars 215 Reviews
Eye Piece Lens Description	NO
Field Of View	1.71 Degrees
Finderscope	Reflex
Focal Length Description	15 millimeters
Focus Type	Manual Focus
Item Dimensions D x W x H	2.4"D x 2.4"W x 2"H
Item Weight	2.08 ounces
Manufacturer	SVBONY
Manufacturer Part Number	FUSF9160A
Model Name	FUSF9160A
Model Number	FUSF9160A
Mount	M42x0.75
Objective Lens Diameter	20 Millimeters
Optical Tube Length	20 Millimeters
Optical-Tube Length	20 Millimeters
Telescope Mount Description	M42x0.75
UPC	609378746406
Warranty Description	We provide 1 year warranty for SVBONY telescope accessories and 30 days no reason to return. Beyond the warranty period: We still offer maintain service, buyers are required to afford corresponding costs. We processed in the most hassle-free way possible.You just need to contact with us on Amazon ,we will reply you within 12 hours

SVBONY M42 Extension Tube Kit on Both Sides (5/10/ 15/ 20mm) | Fully Metal Construction, T2 Interior Thread and T2 Exterior Thread, Freely Combinable M42 Extension Tube

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