Grundig TK 145 Reel to reel tape recorder from 1967 belt dimensions

I assume the answer you already have has suited you, but as a rule of thumb here is how to gauge its length. Take a piece of thread and run it round the pullies three times - snugly not tight or stretched. Cut it at the final overlap. Lay it out and measure its length. Divide that length measurement by three to get your real length.

Suppose that real length is 100mm. To get the diameter of drive belt you need, you divide 100mm by Pi (3.142) which gives you 32 (so a 32mm dia belt). As drive belts must be a 'snug' fit, reduce the diameter (32) by 10% (3mm) and this gives you 29 so you end up looking for a 29mm dia belt. In terms of the belts cross section, again, the rule of thumb is 1mm for small stuff, 1.5mm for bigger and 2mm for more heavy duty needs. Too small a cross section will almost always drive okay but sometimes staring up or slowing down can take a little time to settle out.

Hope that helps   

One is D92 x d2, another one D130 d2, i don't remember which where. O-Ring store or industrial drive components suppliers can help.