Includes the original case, leather strap, and set of four original filters. Excellent condition. 

These are Russian built "maksutov" mirror lenses, production started in the 1950's and continued until the end of the USSR. There are several different models. Online posts indicate the original MTO is an exacta mount, and a different, slimmer body, and was made by KMZ. Then subsequently there was a M39 screw thread mount lens with a 45.2mm registration distance (but infinity focus is normally achievable with just a simple 39-42mm adapter). This thread notes that actual t-mount ones were made for export in the late1960's. Otherwise the LZOS made 3M-5A is the soviet style "t-mount" - the mount will remove to leave a mounting like the internal collar of a standard t-mount. Other t-rings can then be fitted, though there is a mix 'n match process to find one that is the same size internally. Note that there is no M42 x 0.75 thread - don't try to unscrew the mount. 

The 3M-5A was superceded by the 3M-5CA - a lighter design that dispensed with the hood and tripod mount collar (pic 4). That was finally superceded by a lighter more modern design with plastic parts - the ZM-5A.
Pics 1, 2 are of a 3M-5A; pic 3 of a classic MTO with the large mirror housing. Note the early MTO particularly can have problems mounting on dslr due to that large mirror housing/tripod mount ring coming up against the protruding prism housing on many cameras.
Much less common is a very similar MTO 550mm f8.5.
There is also a 3M-6A (=/similar to rubinar? ) 500mm f5.6.

Filter size: 77mm (MTO/3M-5A); 72mm - later designs.
Weight: MTO =1225g; 3M-5CA =620g;  
SIze: MTO ~15.5cm;
Close focus: 4m;
Focus throw: ; focuses past infinity.
MTO/3M-5A: two lens collar mount points, one for portrait and one for landscape, each 1 x 1/4" 1 x 3/8".
Hood: built in retractable.
A full set is a cased lens with 4 filters, orange, green, UV and a NC type filter.