RL: struct mib_entry question

typedef struct mib_entry {
    /* << SNMP-MIB Entry Info >>                */
U8   Type;   /* Object Type                     */
U8   OidLen; /* Object ID length                */
U8   Oid[MIB_OIDSZ];  /* Object ID value */
U8   ValSz;          /* Size of a Variable      */
void *Val;   /* Pointer to a variable           */
void (*cb_func)(int mode);
} MIB_ENTRY;

Why OID has type unsigned char? Numbers in OID can be more than 256.