When it comes to attaching telescopes to mounts, two standards have been established: the relatively narrow rails introduced by the Japanese manufacturer Vixen and the wider Losmandy rails. The latter are 3 inches wide and are mainly used for heavy telescopes.
Most telescope manufacturers follow these standards. Losmandy in particular also offers accessories that follow the Vixen standard.

Astroprints
Vixen-Style dovetail bar for ZWO Seestar 60mm
$ 31.90
ready for shipping in 24
h

Astroprints
Vixen-Style Prism rail for ZWO Seestar 90mm
$ 35.90
ready for shipping in 24
h

Omegon
180mm prism rail with screw
( 5 / 5 )
$ 59.00
ready for shipping in 24
h

Omegon
120mm prism rail
( 1 / 5 )
$ 29.90
ready for shipping in 24
h

Skywatcher
335mm Vixen prism rail
$ 37.90
ready for shipping in 24
h

Astroprints
Mounting for ZWO ASIAIR Plus and Mini on Vixen dovetail bars
$ 29.90
ready for shipping in 24
h

PrimaLuceLab
Prismenschiene PLUS Vixen-Style 240mm
$ 70.00
ready for shipping in 24
h

Artesky
Vixen-Style Prism clamp 150mm
$ 58.00
ready for shipping in 24
h

Bresser
Dovetail clamp Messier Vixen-Style
$ 46.90
ready for shipping in 24
h

Omegon
Pro RC 6" Prism Rail
RRP:
$ 79.00
Our price:
$ 64.90
ready for shipping in 24
h

TS Optics
Vixen-Style Premium Prism Clamp
$ 64.00
ready for shipping in 3-7
days

ASToptics
Universal V-style camera dovetail, 120mm
$ 70.00
ready for shipping in 24
h

Omegon
Mounting Rail 33cm for EQ-4/5/6 Mounts
( 4 / 5 )
$ 39.90
ready for shipping in 24
h

Omegon
Mounting Rail for EQ-4/5/6 Mounts
$ 29.90
ready for shipping in 24
h

Baader
V(EQ) dovetail bar for Celestron 8" SC / HD, orange anodised
$ 87.00
ready for shipping in 1-2
weeks

ASToptics
Universal Vixen-style dovetail, 300mm
$ 106.00
ready for shipping in 24
h

TS Optics
Guidemount - ultra-compact Vixen GP level dual mount
$ 80.00
ready for shipping in 3-7
days

Astroprints
Vixen style prism rail 200mm
$ 54.00
ready for shipping in 24
h

Artesky
Vixen-Style Prism clamp 80mm
$ 51.00
ready for shipping in 24
h

ADM
Prism clamp for Skywatcher AZ-GTI Mount
$ 140.00
ready for shipping in 24
h

Baader
V-Dovetail, 495 mm for Celestron RASA 8"
$ 91.00
ready for shipping in 24
h

Skywatcher
Mounting plate for EQ-4/5/6 mounts - short
$ 30.90
ready for shipping in 1-2
weeks

Lunt Solar Systems
Prism rail, 150mm
$ 101.00
ready for shipping in 24
h

ASToptics
MINI Vixen-style dovetail, 42mm
$ 41.90
ready for shipping in 24
h

Omegon
Premium clamp
$ 79.00
ready for shipping in 24
h

ASToptics
UNIVERSAL V PLATE, 215MM with 50MM PLATFORM (RED)
$ 117.00
ready for shipping in 24
h

TS Optics
Prism clamp Premium XL Vixen-Style
$ 77.00
ready for shipping in 3-7
days

Astroprints
Vixen style prism rail 200mm
$ 54.00
ready for shipping in 24
h

TS Optics
L Bracket
RRP:
$ 106.00
Our price:
$ 71.00
ready for shipping in 1-2
weeks

ADM
Vixen-Style Prism rail for RASA 8" SCT
$ 220.00
ready for shipping in 24
h

Skywatcher
Mounting plate for EQ-3 and EQ-5 mounts, 15cm
$ 27.90
ready for shipping in 24
h

Lacerta
Premium Dovetail Clamp Vixen-Level 63mm
$ 59.00
ready for shipping in 1-2
weeks

Geoptik
Vixen-Style prism rail for Celestron C8 telescope, with two mounting brackets
$ 117.00
ready for shipping in 24
h

William Optics
Vixen-Style 90mm Prism Clamp
$ 117.00
ready for shipping in 24
h

TS Optics
L-Bracket for binoculars and spotting scopes
$ 91.00
ready for shipping in 3-7
days

TS Optics
short full aluminum - prism rail with screw
$ 32.90
ready for shipping in 3-7
days