A Standby Letter of Credit (SBLC) or Bank Guarantee (BG) is usually the SWIFT message MT760; which is a free text message format. SBLC using MT700/701 or MT710/711 (third party bank) is also possible. Most of the technicalities in issuing and executing a SBLC/BG are the same as for Documentary Letter of Credit. In the USA banks are not allowed to work with bank guarantees (BG).
The major difference between Documentary Letter of Credit and Standby Letter of Credits or Bank Guarantee is that SBLC and BG are no payment instrument. It is a “default” guarantee only to be executed in the event that the payment is not being executed as agreed upon. The typical way to do the actual payment is by T/T (MT103). That is the reason why a SBLC or BG will almost never be revolving; instead, the SBLC or BG is open for the full contract term; and the contract will simply be terminated if the SBLC or BG is being drawn; (to the full extent of the value of the guarantee).
SBLC and BG have the advantage over DLC that the value is usually only for one (months) shipment; and therefore requires much less credit line than a revolving DLC; which requires credit line for the full contract value. But of course, this also makes the SBLC or BG a weaker guarantee for continued executing of the contract in favor of the seller/supplier.
Same a DLC might be transferable a SBLC or BG might be transferable. However, as being a guarantee and not a conditional payment instrument; the banks are much more unlikely to accept the status of being transferred as the same as the transferring bank cannot be held countable for the guarantee.