Let me start by saying that I don't know the answer to your question (I've never pulled the starter myself), but here's some information that might help you work it out.
Suzuki uses the JIS (Japanese Industrial Standard) for bolts. It differs a bit from other metric standards in that it uses finer threads and smaller bolt-head sizes. There's a good chart at: Bolt Depot - Common Metric Thread Pitches - Standard, Fine, Super Fine, JIS
Most common Samurai bolts are either 6, 8 or 10mm. (There's a few larger ones on the frame. )
Comparing metric to US sizes:
6mm is close to 1/4", takes a 10mm wrench
8mm is close to 5/16", JIS takes a 12mm wrench
10mm is close to 3/8", JIS takes a 14mm wrench
Common hardware-store metric bolts will likely have 13mm heads on 8mm bolts and 17 mm heads on 10mm bolts. I prefer to use JIS sizes so that I don't have to carry all the odd tool sizes on the trail.
Most all Suzuki bolts are metric Class 8.8, equivalent to US grade 5 strength. They are often head-stamped with a numeral "4". A very few, notably drive shaft bolts, are high strength and head-stamped "7", which is Class 10.9, equivalent to US Grade 8. There's no harm in using stronger bolts, contrary to what you might hear from some un-knowledgeable sources. I occasionally hear of broken Samurai locking front hub bolts, so I replaced them during routine maintenance with the next stronger class 10.9 flange bolts, but keeping to JIS head sizes for tool commonality. There's a hardware discussion and torque values in the downloadable FSM. Try geckocycles and suzukiinfo for starters.
This could be a good time to add a flexible, braided ground strap from the starter to the chassis/frame. A lot of common Samurai grounding problems can be avoided this way.